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❓Given ( x^{2}+y^{2} leqslant 1, a^{2}+b^{2} leqslant 2, x, y, a, b in mathbf{R} ). Prove that ( left|bleft(x^{2}-y^{2}right)+2 a x yright| leqslant sqrt{2} ).
💡Alright, so I've got this inequality to prove: ( left|bleft(x^{2}-y^{2}right)+2 a x yright| leqslant sqrt{2} ). The conditions given are ( x^{2}+y^{2} leqslant 1 ) and ( a^{2}+b^{2} leqslant 2 ), with all variables being real numbers. Hmm, okay. Let me try to unpack this step by step.First, I notice that the expression inside the absolute value looks a bit like something that could come from complex numbers. Specifically, if I think of ( x + yi ) as a complex number, squaring it might give me something similar to ( x^2 - y^2 + 2xyi ). That seems similar to the expression we have, except here it's multiplied by ( b ) and ( a ) respectively. Maybe there's a connection here with complex numbers?Let me write that down. If ( z = x + yi ), then ( z^2 = (x + yi)^2 = x^2 - y^2 + 2xyi ). So, the real part is ( x^2 - y^2 ) and the imaginary part is ( 2xy ). Interesting. Now, if I multiply this by another complex number, say ( w = a + bi ), what do I get?Multiplying ( z^2 ) and ( w ) would give ( z^2 w = (x^2 - y^2 + 2xyi)(a + bi) ). Let me expand this:( (x^2 - y^2)a + (x^2 - y^2)bi + 2xyi a + 2xyi bi ).Simplifying each term:1. ( (x^2 - y^2)a ) is straightforward.2. ( (x^2 - y^2)bi ) is the imaginary part from the first term.3. ( 2xyi a ) is another imaginary term.4. ( 2xyi bi ) becomes ( 2xy b i^2 ), and since ( i^2 = -1 ), this is ( -2xy b ).So, combining like terms:Real part: ( (x^2 - y^2)a - 2xy b ).Imaginary part: ( (x^2 - y^2)b + 2xy a ).Wait a second, the imaginary part is exactly the expression we're supposed to bound: ( b(x^2 - y^2) + 2axy ). So, the expression inside the absolute value is the imaginary part of the product ( z^2 w ).Now, if I recall correctly, the modulus of a complex number is greater than or equal to the absolute value of its imaginary part. That is, for any complex number ( c + di ), ( |c + di| geq |d| ). So, ( |z^2 w| geq |text{Im}(z^2 w)| ).Given that, if I can find an upper bound for ( |z^2 w| ), that will give me an upper bound for ( |text{Im}(z^2 w)| ), which is exactly what I need.So, let's compute ( |z^2 w| ). The modulus of a product is the product of the moduli, so ( |z^2 w| = |z^2| cdot |w| ).First, ( |z| = sqrt{x^2 + y^2} leq 1 ) by the given condition. Therefore, ( |z^2| = |z|^2 leq 1^2 = 1 ).Next, ( |w| = sqrt{a^2 + b^2} leq sqrt{2} ) as given.Multiplying these together, ( |z^2 w| leq 1 times sqrt{2} = sqrt{2} ).Since ( |z^2 w| geq |text{Im}(z^2 w)| ), it follows that ( |text{Im}(z^2 w)| leq |z^2 w| leq sqrt{2} ).Therefore, ( left|bleft(x^{2}-y^{2}right)+2 a x yright| leqslant sqrt{2} ), which is exactly what we needed to prove.Wait, did I just go through the entire proof? Hmm, let me double-check to make sure I didn't skip any steps or make any mistakes.1. Defined ( z = x + yi ) and ( w = a + bi ).2. Calculated ( z^2 = x^2 - y^2 + 2xyi ).3. Multiplied ( z^2 ) by ( w ) and separated real and imaginary parts.4. Identified that the imaginary part is the expression we need to bound.5. Used the property that the modulus of a complex number is at least the absolute value of its imaginary part.6. Calculated ( |z^2 w| ) using the given bounds on ( |z| ) and ( |w| ).7. Concluded that the imaginary part is bounded by ( sqrt{2} ).Everything seems to check out. I think this approach using complex numbers simplifies the problem nicely. It's interesting how representing the expressions as complex numbers can make the relationships clearer and the proof more straightforward.I wonder if there's another way to approach this without using complex numbers, maybe by using inequalities like Cauchy-Schwarz or by completing the square. Let me think about that for a moment.If I try to use the Cauchy-Schwarz inequality, I would need to express the expression ( b(x^2 - y^2) + 2axy ) as a dot product of two vectors. Let's see:Let me denote vector ( mathbf{u} = (b, 2a) ) and vector ( mathbf{v} = (x^2 - y^2, xy) ). Then, the expression becomes ( mathbf{u} cdot mathbf{v} ).By the Cauchy-Schwarz inequality, ( |mathbf{u} cdot mathbf{v}| leq ||mathbf{u}|| cdot ||mathbf{v}|| ).Calculating ( ||mathbf{u}|| = sqrt{b^2 + (2a)^2} = sqrt{b^2 + 4a^2} ).Calculating ( ||mathbf{v}|| = sqrt{(x^2 - y^2)^2 + (xy)^2} ).Hmm, let's compute ( ||mathbf{v}|| ):( (x^2 - y^2)^2 + (xy)^2 = x^4 - 2x^2 y^2 + y^4 + x^2 y^2 = x^4 - x^2 y^2 + y^4 ).Is there a way to bound this expression? Since ( x^2 + y^2 leq 1 ), maybe we can express ( x^4 + y^4 ) in terms of ( (x^2 + y^2)^2 ).Indeed, ( (x^2 + y^2)^2 = x^4 + 2x^2 y^2 + y^4 ), so ( x^4 + y^4 = (x^2 + y^2)^2 - 2x^2 y^2 leq 1 - 2x^2 y^2 ).Therefore, ( ||mathbf{v}||^2 = x^4 - x^2 y^2 + y^4 = (x^4 + y^4) - x^2 y^2 leq (1 - 2x^2 y^2) - x^2 y^2 = 1 - 3x^2 y^2 ).Hmm, this seems a bit messy. I'm not sure if this approach will lead me to the desired bound of ( sqrt{2} ). Maybe the complex number approach was more straightforward after all.Alternatively, perhaps I can consider using trigonometric identities. Since ( x^2 + y^2 leq 1 ), I can parameterize ( x ) and ( y ) using trigonometric functions. Let me try that.Let ( x = r cos theta ) and ( y = r sin theta ), where ( 0 leq r leq 1 ) and ( 0 leq theta < 2pi ).Then, ( x^2 - y^2 = r^2 (cos^2 theta - sin^2 theta) = r^2 cos 2theta ).Similarly, ( 2xy = 2 r cos theta cdot r sin theta = 2 r^2 sin theta cos theta = r^2 sin 2theta ).So, the expression becomes:( b(x^2 - y^2) + 2axy = b r^2 cos 2theta + 2a r^2 sin theta cos theta ).Wait, but ( 2axy = 2a r cos theta cdot r sin theta = 2a r^2 sin theta cos theta = a r^2 sin 2theta ).So, actually, the expression is:( b r^2 cos 2theta + a r^2 sin 2theta ).Factor out ( r^2 ):( r^2 (b cos 2theta + a sin 2theta) ).Now, the expression inside the absolute value is ( r^2 (b cos 2theta + a sin 2theta) ).So, ( |r^2 (b cos 2theta + a sin 2theta)| = r^2 |b cos 2theta + a sin 2theta| ).Since ( r leq 1 ), ( r^2 leq 1 ). Therefore, ( r^2 |b cos 2theta + a sin 2theta| leq |b cos 2theta + a sin 2theta| ).Now, I need to bound ( |b cos 2theta + a sin 2theta| ). This looks like a linear combination of sine and cosine, which can be expressed as a single sine or cosine function with a phase shift.Recall that ( A cos phi + B sin phi = C cos(phi - delta) ), where ( C = sqrt{A^2 + B^2} ) and ( delta = arctan(B/A) ).Applying this to ( b cos 2theta + a sin 2theta ), we get:( sqrt{b^2 + a^2} cos(2theta - delta) ), where ( delta = arctan(a/b) ).Therefore, ( |b cos 2theta + a sin 2theta| leq sqrt{a^2 + b^2} ).Given that ( a^2 + b^2 leq 2 ), this implies ( |b cos 2theta + a sin 2theta| leq sqrt{2} ).Therefore, combining everything:( |b(x^2 - y^2) + 2axy| = r^2 |b cos 2theta + a sin 2theta| leq r^2 sqrt{2} leq sqrt{2} ).Since ( r^2 leq 1 ), the inequality holds.Okay, so using trigonometric parameterization also leads me to the same conclusion. That's reassuring.I think both approaches—the complex number method and the trigonometric parameterization—are valid and lead to the desired result. The complex number approach feels a bit more elegant because it directly relates the expression to the imaginary part of a product, making the modulus properties applicable without much additional work.Just to make sure, let me consider specific cases to test the inequality.**Case 1:** Let ( x = 1 ), ( y = 0 ), ( a = sqrt{2} ), ( b = 0 ).Then, ( x^2 + y^2 = 1 leq 1 ), and ( a^2 + b^2 = 2 leq 2 ).Compute the expression:( b(x^2 - y^2) + 2axy = 0(1 - 0) + 2 times sqrt{2} times 1 times 0 = 0 ).So, ( |0| = 0 leq sqrt{2} ). Okay, holds.**Case 2:** Let ( x = 0 ), ( y = 1 ), ( a = 0 ), ( b = sqrt{2} ).Then, ( x^2 + y^2 = 1 leq 1 ), and ( a^2 + b^2 = 2 leq 2 ).Compute the expression:( b(x^2 - y^2) + 2axy = sqrt{2}(0 - 1) + 2 times 0 times 0 times 1 = -sqrt{2} ).So, ( |-sqrt{2}| = sqrt{2} leq sqrt{2} ). Holds.**Case 3:** Let ( x = frac{1}{sqrt{2}} ), ( y = frac{1}{sqrt{2}} ), ( a = 1 ), ( b = 1 ).Check constraints:( x^2 + y^2 = frac{1}{2} + frac{1}{2} = 1 leq 1 ).( a^2 + b^2 = 1 + 1 = 2 leq 2 ).Compute the expression:( b(x^2 - y^2) + 2axy = 1left(frac{1}{2} - frac{1}{2}right) + 2 times 1 times frac{1}{sqrt{2}} times frac{1}{sqrt{2}} ).Simplify:( 1 times 0 + 2 times frac{1}{2} = 0 + 1 = 1 ).So, ( |1| = 1 leq sqrt{2} ). Holds.**Case 4:** Let ( x = frac{sqrt{3}}{2} ), ( y = frac{1}{2} ), ( a = 1 ), ( b = 1 ).Check constraints:( x^2 + y^2 = frac{3}{4} + frac{1}{4} = 1 leq 1 ).( a^2 + b^2 = 1 + 1 = 2 leq 2 ).Compute the expression:( b(x^2 - y^2) + 2axy = 1left(frac{3}{4} - frac{1}{4}right) + 2 times 1 times frac{sqrt{3}}{2} times frac{1}{2} ).Simplify:( 1 times frac{1}{2} + 2 times frac{sqrt{3}}{4} = frac{1}{2} + frac{sqrt{3}}{2} approx 0.5 + 0.866 = 1.366 ).So, ( |1.366| approx 1.366 leq sqrt{2} approx 1.414 ). Holds.**Case 5:** Let ( x = frac{sqrt{2}}{2} ), ( y = frac{sqrt{2}}{2} ), ( a = 1 ), ( b = 1 ).Wait, this is similar to Case 3. Let me compute it:( x^2 + y^2 = frac{2}{4} + frac{2}{4} = 1 ).( a^2 + b^2 = 1 + 1 = 2 ).Expression:( 1left(frac{2}{4} - frac{2}{4}right) + 2 times 1 times frac{sqrt{2}}{2} times frac{sqrt{2}}{2} = 0 + 2 times frac{2}{4} = 0 + 1 = 1 ).Same as Case 3.**Case 6:** Let me try to maximize the expression. Suppose ( x = cos theta ), ( y = sin theta ), ( a = sqrt{2} cos phi ), ( b = sqrt{2} sin phi ).Then, ( x^2 + y^2 = 1 ), ( a^2 + b^2 = 2 ).Expression becomes:( b(x^2 - y^2) + 2axy = sqrt{2} sin phi (cos^2 theta - sin^2 theta) + 2 times sqrt{2} cos phi times cos theta sin theta ).Simplify:( sqrt{2} sin phi cos 2theta + sqrt{2} cos phi sin 2theta ).Factor out ( sqrt{2} ):( sqrt{2} (sin phi cos 2theta + cos phi sin 2theta) = sqrt{2} sin(2theta + phi) ).The maximum value of ( sin(2theta + phi) ) is 1, so the maximum of the expression is ( sqrt{2} times 1 = sqrt{2} ).Therefore, the maximum possible value of the expression is indeed ( sqrt{2} ), which occurs when ( sin(2theta + phi) = 1 ).This confirms that the inequality ( left|bleft(x^{2}-y^{2}right)+2 a x yright| leqslant sqrt{2} ) holds, and the bound is tight.In summary, by representing the variables as complex numbers or by parameterizing them using trigonometric functions, I was able to leverage properties of moduli and trigonometric identities to establish the desired inequality. The key insight was recognizing the structure of the expression and connecting it to known mathematical concepts that could simplify the proof.I think I've covered multiple approaches and verified the result with specific examples. This gives me confidence that the inequality is indeed valid under the given conditions.
❓A nonzero polynomial with rational coefficients has all of the numbers [1+sqrt[3]{2}, ; 2+sqrt[3]{3}, ;3+sqrt[3]{4},; dots, ;100+sqrt[3]{101}] as roots. What is the smallest possible degree of such a polynomial?
💡Okay, so I have this problem here where I need to find the smallest possible degree of a nonzero polynomial with rational coefficients that has all these numbers (1+sqrt[3]{2}, ; 2+sqrt[3]{3}, ;3+sqrt[3]{4},; dots, ;100+sqrt[3]{101}) as roots. Hmm, that's quite a list of roots! Let me try to break this down step by step.First, I remember that if a polynomial has rational coefficients, then for any irrational root, its conjugate roots must also be included. For example, if (a + bsqrt{c}) is a root, then (a - bsqrt{c}) must also be a root. But in this case, we're dealing with cube roots instead of square roots. So, I need to think about how that affects the roots.Cube roots are a bit trickier because they have more conjugates. Specifically, for a cube root (sqrt[3]{d}), the minimal polynomial over the rationals is (x^3 - d), which has three roots: (sqrt[3]{d}), (omegasqrt[3]{d}), and (omega^2sqrt[3]{d}), where (omega) is a primitive cube root of unity. These are complex numbers, so they aren't just simple conjugates in the real number sense.So, for each (n + sqrt[3]{n+1}), I need to include not just the real root but also the two complex conjugate roots. That means each original root (n + sqrt[3]{n+1}) actually comes with two more roots: (n + omegasqrt[3]{n+1}) and (n + omega^2sqrt[3]{n+1}). Therefore, each of these 100 roots contributes three roots to the polynomial.Let me check if any of these (n + sqrt[3]{n+1}) could be rational. If (n+1) is a perfect cube, then (sqrt[3]{n+1}) would be an integer, making (n + sqrt[3]{n+1}) an integer as well. But looking at the range from (n = 1) to (n = 100), (n+1) ranges from 2 to 101. The perfect cubes in that range are (1^3 = 1), (2^3 = 8), (3^3 = 27), (4^3 = 64), and (5^3 = 125). But 125 is beyond 101, so the perfect cubes within 2 to 101 are 8, 27, and 64. That means when (n+1 = 8), (n = 7); when (n+1 = 27), (n = 26); and when (n+1 = 64), (n = 63). So, for (n = 7), (26), and (63), the term (sqrt[3]{n+1}) is an integer, making (n + sqrt[3]{n+1}) an integer. But in the problem statement, these are still considered roots of the polynomial. However, since the polynomial has rational coefficients, if an integer is a root, it doesn't require any additional conjugate roots because it's already rational. Wait a second, does that mean for (n = 7), (26), and (63), we don't need to include the complex conjugates? Because those roots are already rational. So, for these specific (n) values, instead of contributing three roots each, they only contribute one root each. That would reduce the total number of roots by two for each of these cases.Let me calculate how many such (n) there are. From earlier, I found that (n = 7), (26), and (63) are the cases where (n + sqrt[3]{n+1}) is rational. So that's three values of (n). Each of these would only contribute one root instead of three. Therefore, the total number of roots contributed by these three cases is 3, instead of 9.So, originally, without considering these cases, we would have 100 roots each contributing three roots, totaling 300. But since three of these contribute only one root each, we subtract 2 roots for each of these three cases. That is, 300 - (3 * 2) = 300 - 6 = 294.Wait, but hold on. Let me think again. If (n + sqrt[3]{n+1}) is rational, then it's a root, but does that mean the minimal polynomial for that root is just a linear factor, right? So, instead of having a cubic factor, we have a linear factor. So, for each such (n), instead of degree 3, we have degree 1. So, the total degree would be 3*(100 - 3) + 1*3 = 3*97 + 3 = 291 + 3 = 294.But wait, hold on. The minimal polynomial for each (n + sqrt[3]{n+1}) is degree 3 unless (sqrt[3]{n+1}) is rational, in which case the minimal polynomial is degree 1. So, for each (n) where (n+1) is a perfect cube, the minimal polynomial is degree 1, otherwise, it's degree 3.So, the total degree would be 3*(number of non-perfect cube terms) + 1*(number of perfect cube terms). We have 100 terms in total, 3 of which are perfect cubes (n=7,26,63). So, 3*(100 - 3) + 1*3 = 3*97 + 3 = 291 + 3 = 294.But wait, is that correct? Because each non-perfect cube term contributes 3 roots, and each perfect cube term contributes 1 root. So, total roots would be 3*(100 - 3) + 1*3 = 294. Therefore, the minimal polynomial would have degree 294.But hold on, in the initial problem statement, it says "a nonzero polynomial with rational coefficients has all of the numbers... as roots." So, does that mean that the polynomial must have all these numbers as roots, but not necessarily that it's the minimal polynomial? Or is it asking for the minimal polynomial?Wait, the question is asking for the smallest possible degree of such a polynomial. So, it's the minimal polynomial that includes all these roots. Therefore, the minimal polynomial would have degree equal to the sum of the degrees of the minimal polynomials of each root, but considering overlaps.But wait, actually, if the roots are all distinct and their minimal polynomials are irreducible over Q, then the minimal polynomial would be the product of these minimal polynomials, hence the degree would be the sum of their degrees.But in this case, for each (n + sqrt[3]{n+1}), the minimal polynomial is either degree 1 or degree 3. So, if we have 100 roots, 3 of which have minimal polynomial degree 1, and 97 of which have minimal polynomial degree 3, then the total degree would be 3*97 + 1*3 = 294.But wait, is that correct? Because each minimal polynomial for the non-perfect cube terms is degree 3, but are these minimal polynomials distinct? Or could they potentially share factors?Hmm, that's a good point. If two different (n + sqrt[3]{n+1}) have the same minimal polynomial, then the total degree would be less because we wouldn't need to multiply by separate factors. But I don't think that's the case here.Each minimal polynomial for (n + sqrt[3]{n+1}) is ( (x - (n + sqrt[3]{n+1}))(x - (n + omegasqrt[3]{n+1}))(x - (n + omega^2sqrt[3]{n+1})) ). These are distinct for each (n) because (n) is different each time, and (sqrt[3]{n+1}) is different for each (n). Therefore, each minimal polynomial is distinct and irreducible over Q. So, the total degree is indeed the sum of their degrees.Therefore, the minimal polynomial would have degree 3*(100 - 3) + 1*3 = 294.But wait, let me think again. The minimal polynomial for each (n + sqrt[3]{n+1}) is degree 3 unless (n+1) is a perfect cube, in which case it's degree 1. So, for each of the 97 non-perfect cube terms, we have degree 3, and for the 3 perfect cube terms, we have degree 1. So, total degree is 97*3 + 3*1 = 291 + 3 = 294.But wait, in the initial problem, the user wrote:"A nonzero polynomial with rational coefficients has all of the numbers [1+sqrt[3]{2}, ; 2+sqrt[3]{3}, ;3+sqrt[3]{4},; dots, ;100+sqrt[3]{101}] as roots. What is the smallest possible degree of such a polynomial?"So, the answer is 300, but in my calculation, it's 294. But wait, in the initial assistant answer, it was 300, but I think that was incorrect because it didn't account for the perfect cube cases.Wait, let me check again. For n from 1 to 100, n+1 from 2 to 101. The perfect cubes in that range are 8, 27, 64, and 125. But 125 is beyond 101, so only 8, 27, 64. Therefore, n = 7, 26, 63.So, for these three n's, the minimal polynomial is degree 1, and for the rest, it's degree 3. Therefore, total degree is 3*(100 - 3) + 1*3 = 294.But wait, in the initial assistant answer, it said 300, but that didn't consider the perfect cube cases. So, is the correct answer 294?Wait, but let me think again. Is the minimal polynomial for each (n + sqrt[3]{n+1}) actually irreducible over Q? Or could they potentially share some factors?I think they are irreducible because each minimal polynomial is a cubic with coefficients in Q, and since (sqrt[3]{n+1}) is not rational, the minimal polynomial is indeed degree 3. So, each non-perfect cube term contributes 3 to the degree, and each perfect cube term contributes 1.Therefore, the total degree is 3*(100 - 3) + 1*3 = 294.But wait, let me think about the field extensions. If we adjoin all these roots, does the degree of the extension over Q become 3^100? No, that's not right because the extensions might not be linearly disjoint.But in this case, since each minimal polynomial is irreducible and distinct, the compositum of all these extensions would have degree equal to the product of the degrees, but that's only if they are linearly disjoint, which they are not necessarily.Wait, this is getting complicated. Maybe the minimal polynomial is the product of all these minimal polynomials, each of degree 3 or 1, so the total degree is 294.But I'm not entirely sure. Maybe I should look for a pattern or a simpler case.Let me consider a smaller case. Suppose we have just two roots: (1 + sqrt[3]{2}) and (2 + sqrt[3]{3}). What would be the minimal polynomial for these?For (1 + sqrt[3]{2}), the minimal polynomial is ((x - 1 - sqrt[3]{2})(x - 1 - omegasqrt[3]{2})(x - 1 - omega^2sqrt[3]{2})), which is a cubic.For (2 + sqrt[3]{3}), similarly, the minimal polynomial is another cubic.So, the minimal polynomial for both would be the product of these two cubics, giving degree 6.But wait, is that correct? Or could there be some overlap?I think in this case, since the minimal polynomials are distinct and irreducible, their product would indeed be the minimal polynomial with both roots, giving degree 6.Similarly, if we have three such roots, each contributing a cubic, the total degree would be 9, unless some minimal polynomials share factors, which they don't because the roots are different.Therefore, extrapolating this, for 100 roots, each contributing a cubic, except for three which contribute linear factors, the total degree would be 3*(100 - 3) + 1*3 = 294.But wait, in the initial problem, the user wrote that the answer was 300, but that didn't account for the perfect cube cases. So, perhaps the correct answer is 294.But I'm not entirely sure. Maybe I should double-check.Wait, let me think about the minimal polynomial for (n + sqrt[3]{n+1}). If (n+1) is not a perfect cube, then (sqrt[3]{n+1}) is irrational, and the minimal polynomial is indeed degree 3. If (n+1) is a perfect cube, then (sqrt[3]{n+1}) is rational, so the minimal polynomial is degree 1.Therefore, for each (n), if (n+1) is a perfect cube, the minimal polynomial is degree 1; otherwise, it's degree 3.So, in our case, n ranges from 1 to 100, so n+1 ranges from 2 to 101. The perfect cubes in that range are 8, 27, 64, and 125. But 125 is beyond 101, so only 8, 27, 64. Therefore, n = 7, 26, 63.So, for these three n's, the minimal polynomial is degree 1, and for the other 97 n's, it's degree 3.Therefore, the total degree is 3*97 + 1*3 = 291 + 3 = 294.So, the minimal polynomial would have degree 294.But wait, in the initial assistant answer, it was 300, but that didn't account for the perfect cube cases. So, I think the correct answer is 294.But let me think again. Is there a possibility that some of the minimal polynomials could share factors, thus reducing the total degree? For example, could two different (n + sqrt[3]{n+1}) have the same minimal polynomial?I don't think so, because each minimal polynomial is constructed from a different (n) and a different (sqrt[3]{n+1}). Therefore, they are distinct and irreducible over Q.Therefore, the total degree is indeed 294.Wait, but let me think about the field extensions again. If we adjoin all these roots, the degree of the extension Q((sqrt[3]{2}, sqrt[3]{3}, ldots, sqrt[3]{101})) over Q is 3^100, which is huge. But that's not the case because many of these cube roots are related.Wait, no, actually, each (sqrt[3]{n+1}) is algebraically independent over Q, except for the perfect cubes. So, the degree of the extension would be 3^{100 - 3} = 3^{97}, but that's not directly relevant here because we're considering the minimal polynomial that has all these roots, not the degree of the extension.Wait, perhaps I'm overcomplicating it. The minimal polynomial is the product of the minimal polynomials of each root, each of which is either degree 1 or 3. Therefore, the total degree is 294.But let me think about another angle. Suppose I have a polynomial with rational coefficients that has all these roots. Then, for each (n + sqrt[3]{n+1}), it must have all its conjugates as roots. So, for each non-perfect cube n, we have three roots: (n + sqrt[3]{n+1}), (n + omegasqrt[3]{n+1}), (n + omega^2sqrt[3]{n+1}). For perfect cubes, we only have one root.Therefore, the total number of roots is 3*(100 - 3) + 1*3 = 294. Hence, the minimal polynomial must have degree 294.But wait, in the initial problem, the user wrote that the answer was 300, but that was incorrect because it didn't account for the perfect cube cases. So, the correct answer should be 294.But wait, let me think again. Is the minimal polynomial for each (n + sqrt[3]{n+1}) actually degree 3? Or could it be higher?No, because (sqrt[3]{n+1}) satisfies a cubic equation, so (n + sqrt[3]{n+1}) satisfies a cubic equation as well. Therefore, the minimal polynomial is indeed degree 3.Therefore, the total degree is 3*(100 - 3) + 1*3 = 294.So, I think the correct answer is 294.
❓Carla started with some marbles. She bought 134 marbles and now she has a certain number of marbles. She started with 53 marbles. How many marbles does she have now?
💡First, identify the number of marbles Carla started with, which is 53.Next, determine the number of marbles Carla bought, which is 134.To find the total number of marbles Carla has now, add the initial number of marbles to the number of marbles she bought.So, 53 plus 134 equals 187.Therefore, Carla now has 187 marbles.
❓Given that the lines x=frac{5π}{6} and x=frac{4π}{3} are the adjacent two symmetric axes of the graph of the function f(x)=4sin(ωx+frac{π}{6})(ω>0), shifting the graph of f(x) to the right by frac{π}{6} units results in the graph of a function g(x). If g(x) has exactly three distinct zeros in the interval (-m,m), the range of real number m is ()A: ({frac{7π}{12}},frac{11π}{12}]B: ({frac{7π}{12}},frac{13π}{12}]C: ({frac{5π}{12}},frac{13π}{12}]D: ({frac{5π}{12}},frac{11π}{12}]
💡Alright, let's try to tackle this problem step by step. It's about a sine function with some given symmetries and then shifting it to find the range of m where the shifted function has exactly three zeros in the interval (-m, m). Hmm, okay, let's break it down.First, the function given is f(x) = 4 sin(ωx + π/6), and it's mentioned that the lines x = 5π/6 and x = 4π/3 are adjacent symmetric axes. I remember that for sine functions, the symmetric axes are the vertical lines passing through the maxima and minima. So, these lines are essentially the midlines between the peaks and troughs of the sine wave.Since these are adjacent symmetric axes, the distance between them should be half the period of the function. Let me calculate the distance between x = 5π/6 and x = 4π/3.Calculating the difference: 4π/3 - 5π/6. To subtract these, I need a common denominator. 4π/3 is equal to 8π/6, so 8π/6 - 5π/6 = 3π/6 = π/2. So, the distance between these two symmetric axes is π/2, which is half the period. Therefore, the full period T is π.Now, the period of a sine function is given by T = 2π / ω. Since we found T = π, we can solve for ω:π = 2π / ω ⇒ ω = 2.Okay, so ω is 2. That means the function f(x) is 4 sin(2x + π/6).Next, we're told that the graph of f(x) is shifted to the right by π/6 units to get g(x). Shifting a function to the right by π/6 means replacing x with x - π/6 in the function. So, let's write g(x):g(x) = 4 sin(2(x - π/6) + π/6) = 4 sin(2x - π/3 + π/6) = 4 sin(2x - π/6).Simplify that: 4 sin(2x - π/6). So, g(x) is 4 sin(2x - π/6).Now, we need to find the range of m such that g(x) has exactly three distinct zeros in the interval (-m, m). So, we need to find the values of m where the function crosses the x-axis three times between -m and m.First, let's find the zeros of g(x). The zeros occur when sin(2x - π/6) = 0. So, 2x - π/6 = kπ, where k is an integer.Solving for x: 2x = kπ + π/6 ⇒ x = (kπ + π/6)/2 = (kπ)/2 + π/12.So, the zeros are at x = (kπ)/2 + π/12 for all integers k.Now, we need to find the values of k such that x is in (-m, m). So, we need to find the number of integers k where (kπ)/2 + π/12 is between -m and m.But since m is positive, we can consider k such that (kπ)/2 + π/12 is in (-m, m). So, we need to find k such that:-m < (kπ)/2 + π/12 < m.Let me rearrange this inequality to solve for k:-m - π/12 < (kπ)/2 < m - π/12.Multiply all parts by 2/π to solve for k:(-2m/π) - (1/6) < k < (2m/π) - (1/6).Since k must be an integer, the number of integers k in this interval will determine the number of zeros.We need exactly three distinct zeros, so there should be exactly three integers k satisfying this inequality.Let's think about how the zeros are spaced. The zeros occur at x = (kπ)/2 + π/12. So, the distance between consecutive zeros is π/2. Therefore, the zeros are spaced π/2 apart.Given that, we need to find m such that the interval (-m, m) contains exactly three zeros. So, the interval should be just large enough to include three zeros but not four.To visualize, let's plot the zeros on the number line. The zeros are at:For k = 0: x = π/12 ≈ 0.2618k = 1: x = π/2 + π/12 = (6π/12 + π/12) = 7π/12 ≈ 1.8326k = -1: x = -π/2 + π/12 = (-6π/12 + π/12) = -5π/12 ≈ -1.3080k = 2: x = π + π/12 = 13π/12 ≈ 3.4002k = -2: x = -π + π/12 = -11π/12 ≈ -2.8798Wait, but we need to consider the interval (-m, m). So, the zeros within this interval would be symmetric around the origin, but since the function is shifted, the zeros might not be symmetric.Wait, actually, the function g(x) = 4 sin(2x - π/6) is a sine function with a phase shift. So, its zeros are not symmetric around the origin. Therefore, the number of zeros in (-m, m) might not be symmetric.Hmm, that complicates things a bit. Maybe I should consider the general approach.We have zeros at x = (kπ)/2 + π/12. Let's list some zeros:For k = -2: x = (-2π)/2 + π/12 = -π + π/12 = -11π/12 ≈ -2.8798k = -1: x = (-π)/2 + π/12 = -5π/12 ≈ -1.3080k = 0: x = π/12 ≈ 0.2618k = 1: x = π/2 + π/12 = 7π/12 ≈ 1.8326k = 2: x = π + π/12 = 13π/12 ≈ 3.4002k = 3: x = 3π/2 + π/12 = 19π/12 ≈ 5.0614And so on.So, the zeros are at approximately:-2.8798, -1.3080, 0.2618, 1.8326, 3.4002, 5.0614,...Now, we need to find m such that in (-m, m), there are exactly three zeros.Looking at the zeros, let's see:If m is just slightly larger than 0.2618, then the interval (-m, m) would include only one zero: 0.2618.Wait, but actually, if m is greater than 0.2618, then the interval (-m, m) would include 0.2618 and -0.2618? Wait, no, because the zeros are not symmetric. The zero at k=0 is at π/12 ≈ 0.2618, and the zero at k=-1 is at -5π/12 ≈ -1.3080.So, if m is between π/12 and 5π/12, then the interval (-m, m) would include the zero at π/12 and the zero at -5π/12, but not the zero at 7π/12 or -11π/12.Wait, let's think carefully.If m is between π/12 and 5π/12, then:- The zero at π/12 is inside (-m, m) if m > π/12.- The zero at -5π/12 is inside (-m, m) if m > 5π/12.Wait, no. If m is greater than π/12, then the interval (-m, m) includes all x such that -m < x < m.So, if m is greater than π/12, then x = π/12 is inside the interval.Similarly, if m is greater than 5π/12, then x = -5π/12 is inside the interval.So, if m is between π/12 and 5π/12, then the interval (-m, m) includes x = π/12 but not x = -5π/12.Wait, no, because m is positive, and -m is negative. So, if m is greater than 5π/12, then -m is less than -5π/12, so x = -5π/12 is greater than -m, hence inside (-m, m).Wait, let me clarify:If m is greater than 5π/12, then -m is less than -5π/12. So, x = -5π/12 is greater than -m, so it's inside (-m, m).Similarly, x = π/12 is less than m, so it's inside.So, if m is greater than 5π/12, then both x = π/12 and x = -5π/12 are inside (-m, m). Additionally, x = 7π/12 is greater than m only if m < 7π/12. Similarly, x = -11π/12 is less than -m only if m > 11π/12.Wait, this is getting a bit confusing. Maybe I should plot the zeros on the number line and see how they fall into the interval (-m, m).Zeros are at:-11π/12 ≈ -2.8798-5π/12 ≈ -1.3080π/12 ≈ 0.26187π/12 ≈ 1.832613π/12 ≈ 3.400219π/12 ≈ 5.0614So, the zeros are spread out on both sides of the origin.Now, we need to find m such that exactly three zeros lie in (-m, m).Looking at the zeros:If m is just greater than π/12, then the interval (-m, m) includes x = π/12 and x = -5π/12? Wait, no, because m is greater than π/12, so -m is less than -π/12. So, x = -5π/12 is less than -π/12, so it's outside the interval (-m, m) if m < 5π/12.Wait, let's think about it:If m is between π/12 and 5π/12:- The interval (-m, m) includes x = π/12 (since m > π/12) and x = -5π/12 is less than -m (since m < 5π/12), so x = -5π/12 is outside.Therefore, in this case, the interval (-m, m) includes only x = π/12.Wait, but that's only one zero. Hmm, that can't be right because we need three zeros.Wait, maybe I'm missing something. Let's consider the zeros:- For k = -2: x = -11π/12 ≈ -2.8798- For k = -1: x = -5π/12 ≈ -1.3080- For k = 0: x = π/12 ≈ 0.2618- For k = 1: x = 7π/12 ≈ 1.8326- For k = 2: x = 13π/12 ≈ 3.4002So, if m is between π/12 and 5π/12:- The interval (-m, m) includes x = π/12 (since m > π/12) and x = -5π/12 is less than -m (since m < 5π/12), so x = -5π/12 is outside.But what about x = 7π/12? 7π/12 is approximately 1.8326, which is greater than m (since m < 5π/12 ≈ 1.3080). So, x = 7π/12 is outside.Similarly, x = -11π/12 is less than -m (since m < 5π/12), so it's outside.Therefore, in this case, only x = π/12 is inside (-m, m). That's only one zero.Wait, that contradicts the earlier thought that m between π/12 and 5π/12 would include x = π/12 and x = -5π/12. But actually, x = -5π/12 is less than -m, so it's outside.So, only x = π/12 is inside.Hmm, so maybe I need to consider higher k values.Wait, let's think differently. Maybe I should consider the number of zeros in (-m, m) as m increases.When m is very small, approaching 0, there are no zeros.As m increases past π/12, we include x = π/12.As m increases past 5π/12, we include x = -5π/12.As m increases past 7π/12, we include x = 7π/12.As m increases past 11π/12, we include x = -11π/12.Wait, let's list the critical points where m crosses a zero:- m = π/12 ≈ 0.2618: includes x = π/12- m = 5π/12 ≈ 1.3080: includes x = -5π/12- m = 7π/12 ≈ 1.8326: includes x = 7π/12- m = 11π/12 ≈ 2.8798: includes x = -11π/12So, let's see how the number of zeros increases as m increases:- For m < π/12: 0 zeros- For π/12 < m < 5π/12: 1 zero (x = π/12)- For 5π/12 < m < 7π/12: 2 zeros (x = π/12 and x = -5π/12)- For 7π/12 < m < 11π/12: 3 zeros (x = π/12, x = -5π/12, x = 7π/12)- For m > 11π/12: 4 zeros (x = π/12, x = -5π/12, x = 7π/12, x = -11π/12)Wait, but the problem says "exactly three distinct zeros". So, according to this, when m is between 7π/12 and 11π/12, the interval (-m, m) includes exactly three zeros: π/12, -5π/12, and 7π/12.But wait, when m is between 7π/12 and 11π/12, does x = -11π/12 get included? Because m is less than 11π/12, so -m is greater than -11π/12, so x = -11π/12 is less than -m, hence outside the interval.Similarly, x = 13π/12 is greater than m (since m < 11π/12), so it's outside.Therefore, in the interval (-m, m) when 7π/12 < m < 11π/12, we have three zeros: π/12, -5π/12, and 7π/12.But wait, when m is exactly 7π/12, x = 7π/12 is included, so at m = 7π/12, we have three zeros: π/12, -5π/12, and 7π/12.Similarly, when m is exactly 11π/12, x = -11π/12 is included, so we have four zeros: π/12, -5π/12, 7π/12, and -11π/12.Therefore, to have exactly three zeros, m must be greater than 7π/12 but less than or equal to 11π/12.Wait, but the options given are:A: (7π/12, 11π/12]B: (7π/12, 13π/12]C: (5π/12, 13π/12]D: (5π/12, 11π/12]So, according to my reasoning, the correct range is (7π/12, 11π/12], which is option A.But wait, let me double-check. When m is exactly 7π/12, the interval (-m, m) includes x = 7π/12, so we have three zeros: π/12, -5π/12, and 7π/12.When m is exactly 11π/12, the interval includes x = -11π/12, so we have four zeros. Therefore, m must be strictly greater than 7π/12 and less than or equal to 11π/12.So, the range is (7π/12, 11π/12], which is option A.But wait, the initial calculation of the period might have been incorrect. Let me double-check that.We were given that x = 5π/6 and x = 4π/3 are adjacent symmetric axes. The distance between them is 4π/3 - 5π/6 = (8π/6 - 5π/6) = 3π/6 = π/2.Since these are adjacent symmetric axes, the distance between them is half the period, so the full period is π.Therefore, ω = 2π / T = 2π / π = 2. So, ω = 2, which is correct.Then, f(x) = 4 sin(2x + π/6). Shifting to the right by π/6, we replace x with x - π/6:g(x) = 4 sin(2(x - π/6) + π/6) = 4 sin(2x - π/3 + π/6) = 4 sin(2x - π/6).So, that's correct.Then, zeros at x = (kπ + π/6)/2 = kπ/2 + π/12.So, the zeros are at x = kπ/2 + π/12.So, for k = -2: -π + π/12 = -11π/12k = -1: -π/2 + π/12 = -5π/12k = 0: π/12k = 1: π/2 + π/12 = 7π/12k = 2: π + π/12 = 13π/12So, zeros at -11π/12, -5π/12, π/12, 7π/12, 13π/12,...Therefore, when m is between 7π/12 and 11π/12, the interval (-m, m) includes:- For m > 7π/12: x = 7π/12 is included- For m < 11π/12: x = -11π/12 is excludedSo, zeros inside (-m, m):- x = π/12, x = -5π/12, x = 7π/12That's three zeros.When m = 7π/12, x = 7π/12 is included, so three zeros.When m = 11π/12, x = -11π/12 is included, making four zeros.Therefore, m must be greater than 7π/12 and less than or equal to 11π/12.So, the range is (7π/12, 11π/12], which is option A.But wait, the options are:A: (7π/12, 11π/12]B: (7π/12, 13π/12]C: (5π/12, 13π/12]D: (5π/12, 11π/12]So, option A is correct.Wait, but in the initial problem statement, it's mentioned that the function f(x) has symmetric axes at x = 5π/6 and x = 4π/3. These are the midlines between the peaks and troughs.But in my calculation, I considered the distance between these axes as half the period, which gave me the period as π. But let me confirm that.For a sine function, the distance between two adjacent symmetric axes (which are the midlines between peaks and troughs) is indeed half the period. So, if the distance is π/2, then the full period is π.Therefore, ω = 2π / T = 2π / π = 2, which is correct.So, the function f(x) = 4 sin(2x + π/6), and after shifting right by π/6, we get g(x) = 4 sin(2x - π/6).Zeros at x = kπ/2 + π/12.Therefore, the zeros are at:k = -2: -11π/12k = -1: -5π/12k = 0: π/12k = 1: 7π/12k = 2: 13π/12So, in the interval (-m, m), we need exactly three zeros. As m increases:- For m < π/12: 0 zeros- π/12 < m < 5π/12: 1 zero (π/12)- 5π/12 < m < 7π/12: 2 zeros (π/12, -5π/12)- 7π/12 < m < 11π/12: 3 zeros (π/12, -5π/12, 7π/12)- m > 11π/12: 4 zeros (π/12, -5π/12, 7π/12, -11π/12)Therefore, to have exactly three zeros, m must be in (7π/12, 11π/12].So, the correct answer is option A: (7π/12, 11π/12].
❓Calculate: (1-i)^2 (where i is the imaginary unit).
💡To calculate ((1 - i)^2), I start by expanding the expression using the formula for squaring a binomial: ((a - b)^2 = a^2 - 2ab + b^2).First, I square the first term: (1^2 = 1).Next, I calculate the middle term: (2 times 1 times i = 2i).Then, I square the second term: (i^2 = -1).Combining these results, the expression becomes (1 - 2i + (-1)).Simplifying further, (1 - 1 = 0), so the expression reduces to (-2i).Therefore, the final result of ((1 - i)^2) is (-2i).
❓After a polygon cuts off one angle, the sum of the interior angles of the resulting polygon is 1620^{circ}. What is the number of sides of the original polygon?A: 10B: 11C: 12D: All of the above are possible
💡Okay, so I have this problem here: After a polygon cuts off one angle, the sum of the interior angles of the resulting polygon is 1620 degrees. I need to find the number of sides of the original polygon, and the options are 10, 11, 12, or all of the above are possible.Hmm, let's start by recalling some basics about polygons and their angles. I remember that the sum of the interior angles of an n-sided polygon is given by the formula (n-2) × 180 degrees. So, if the resulting polygon has a sum of 1620 degrees, I can set up the equation:(n-2) × 180 = 1620Let me solve for n:First, divide both sides by 180:(n-2) = 1620 / 180Calculating that, 1620 divided by 180 is 9.So, n - 2 = 9Therefore, n = 11Okay, so the resulting polygon has 11 sides. But the question is about the original polygon before it cut off one angle. So, I need to think about how cutting off one angle affects the number of sides.From what I remember, when you cut off a corner (or an angle) of a polygon, you can either:1. Remove one side and add two sides, effectively increasing the number of sides by one.2. Remove one side and add one side, keeping the number of sides the same.3. Remove two sides and add one side, decreasing the number of sides by one.Wait, is that right? Let me visualize it.Imagine a simple polygon, like a square. If I cut off one corner, depending on where I cut, I can either:- Cut from one side to another, which would replace one side with two sides, increasing the total number of sides by one.- Or, if I cut in such a way that it only replaces a vertex without adding extra sides, keeping the number of sides the same.- Or, if I cut in a way that removes a side, but I'm not sure if that's possible without changing the overall structure too much.Hmm, maybe I should think in terms of how the number of sides changes when you truncate a corner.If you have a polygon with n sides and you cut off one corner, you're essentially replacing one vertex with a new edge. Depending on how you do this, you can either:- Add one side, making it n + 1 sides.- Keep the number of sides the same, n sides.- Or, subtract one side, making it n - 1 sides.But wait, subtracting a side seems a bit counterintuitive. How would cutting off a corner remove a side? Maybe if you cut in such a way that two sides are merged into one? I'm not entirely sure about that.Let me look up or recall the exact effect of truncating a polygon's corner on the number of sides.After a quick recall, I think that truncating a corner (vertex) of a polygon typically involves cutting off the vertex with a straight line, which replaces the vertex with a new edge. This operation adds one new side to the polygon. So, if you start with an n-sided polygon and truncate one corner, you end up with an (n + 1)-sided polygon.But wait, that contradicts my earlier thought about keeping the number of sides the same or even decreasing it. Maybe it depends on how exactly you truncate the corner.If you make a very small cut near the vertex, you might just replace the vertex with a new edge, effectively adding one side. But if you make a larger cut that intersects two adjacent sides, you might be replacing one side with two sides, which would also increase the number of sides by one.Alternatively, if you cut in such a way that you merge two sides into one, you could potentially decrease the number of sides by one. But I'm not sure if that's a standard way of truncating a corner.Wait, maybe I should think about the different cases:1. **Cutting off a corner without intersecting any other sides:** This would just replace the vertex with a new edge, adding one side. So, n becomes n + 1.2. **Cutting off a corner by intersecting two adjacent sides:** This would replace the corner with a new edge, but also split one side into two, effectively adding one side. So again, n becomes n + 1.3. **Cutting off a corner in a way that merges two sides:** I'm not sure if this is possible without altering the polygon's structure significantly. Maybe in some cases, but it's not the standard way.So, perhaps the most common outcome is that cutting off a corner increases the number of sides by one. Therefore, if the resulting polygon has 11 sides, the original polygon must have had 10 sides.But wait, the answer choices include 10, 11, and 12, and also the option that all of the above are possible. So, maybe there are different ways to cut off a corner that can result in the same number of sides or even increase or decrease the number of sides.Let me think again.If you have a polygon and you cut off a corner:- If you cut in such a way that you replace one side with two sides, you increase the number of sides by one.- If you cut in such a way that you replace one vertex without changing the number of sides, you keep the number of sides the same.- If you cut in such a way that you merge two sides into one, you decrease the number of sides by one.But is merging two sides into one actually possible by just cutting off a corner? I'm not entirely sure.Wait, maybe if you have a polygon and you cut off a corner in such a way that the cut intersects two non-adjacent sides, you could potentially merge two sides into one, thereby decreasing the number of sides by one.But in a convex polygon, all sides are adjacent in a specific order, so cutting off a corner would typically only intersect two adjacent sides, replacing one vertex with a new edge, thus increasing the number of sides by one.However, in a concave polygon, maybe you can have a situation where cutting off a corner could intersect non-adjacent sides, leading to a decrease in the number of sides.But the problem doesn't specify whether the polygon is convex or concave. So, perhaps all three scenarios are possible depending on the type of polygon and how the corner is cut off.Therefore, if the resulting polygon has 11 sides, the original polygon could have had:- 10 sides if cutting off a corner increased the number of sides by one.- 11 sides if cutting off a corner didn't change the number of sides.- 12 sides if cutting off a corner decreased the number of sides by one.Hence, all of the above are possible.Wait, but earlier I thought that cutting off a corner typically increases the number of sides by one. So, why would it keep the same or decrease?Maybe I need to clarify the different ways of cutting off a corner.Case 1: Cutting off a corner by intersecting two adjacent sides. This replaces one vertex with a new edge, increasing the number of sides by one.Case 2: Cutting off a corner in such a way that the cut doesn't intersect any sides, just replaces the vertex. This would keep the number of sides the same.Case 3: Cutting off a corner in a way that intersects two non-adjacent sides, effectively merging two sides into one, thus decreasing the number of sides by one.But in a convex polygon, all sides are adjacent in a cyclic order, so cutting off a corner would only intersect two adjacent sides, leading to an increase in the number of sides.However, in a concave polygon, it's possible that cutting off a corner could intersect non-adjacent sides, leading to a decrease in the number of sides.Therefore, depending on the type of polygon and how the corner is cut off, the number of sides can increase, stay the same, or decrease.Hence, if the resulting polygon has 11 sides, the original polygon could have had 10, 11, or 12 sides.Therefore, the answer is D: All of the above are possible.