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❓Keith picked 3 pears and Jason picked some pears from the pear tree. Joan picked 5 apples from the apple tree. In total, 5 pears were picked. How many pears did Jason pick?
💡First, identify the total number of pears picked, which is 5.Keith picked 3 pears.To find out how many pears Jason picked, subtract the number of pears Keith picked from the total number of pears picked.So, 5 pears minus 3 pears equals 2 pears.Therefore, Jason picked 2 pears.
❓Bob rolls a fair eight-sided die each morning. The numbers on the die are 1, 2, 3, 4, 5, 6, 7, and 8. If he rolls a number that is a multiple of 2, he eats sweetened cereal. If he rolls a number that is a multiple of 3, he eats unsweetened cereal. If he rolls a number that is both, he chooses at random. If he rolls a 1, then he rolls again. In a non-leap year, what is the expected value of the difference between the number of days Bob eats unsweetened cereal and the number of days he eats sweetened cereal?
💡Alright, so I've got this problem about Bob rolling an eight-sided die each morning. Let me try to break it down step by step. First, the die has numbers 1 through 8. If he rolls a multiple of 2, he eats sweetened cereal. If he rolls a multiple of 3, he eats unsweetened cereal. If he rolls a number that's both a multiple of 2 and 3, which is 6 in this case, he chooses randomly between sweetened and unsweetened. Also, if he rolls a 1, he rolls again. I need to find the expected difference between the number of days he eats unsweetened cereal and sweetened cereal in a non-leap year, which has 365 days.Okay, so let's start by figuring out the probabilities of each outcome. The die is eight-sided, so normally, each number has a 1/8 chance. But since rolling a 1 means he rolls again, we need to adjust the probabilities accordingly. Essentially, rolling a 1 is like rolling again, so we can think of it as a geometric distribution where he keeps rolling until he gets a number that's not 1. So, the probability of rolling any number from 2 to 8 is 7/8, and since he keeps rolling until he gets one of those, each number from 2 to 8 has an equal probability of 1/7.Now, let's identify the numbers that are multiples of 2, multiples of 3, and both. Multiples of 2 on the die are 2, 4, 6, and 8. Multiples of 3 are 3 and 6. So, 6 is the only number that's both a multiple of 2 and 3. So, the probability of rolling a multiple of 2 is the number of multiples of 2 divided by 7, which is 4/7. Similarly, the probability of rolling a multiple of 3 is 2/7. The probability of rolling a number that's both is 1/7, which is the probability of rolling a 6.Now, when he rolls a 6, he chooses randomly between sweetened and unsweetened cereal. So, the probability of choosing sweetened is 1/2, and the same for unsweetened. Therefore, we need to adjust the probabilities for sweetened and unsweetened cereal accordingly.Let's define:- P(S) as the probability of eating sweetened cereal.- P(U) as the probability of eating unsweetened cereal.So, P(S) is the probability of rolling a multiple of 2, excluding the overlap with multiples of 3, plus half the probability of rolling a 6. Similarly, P(U) is the probability of rolling a multiple of 3, excluding the overlap with multiples of 2, plus half the probability of rolling a 6.Mathematically, that would be:- P(S) = (Number of multiples of 2 only)/7 + (1/2)*(Number of multiples of both)/7- P(U) = (Number of multiples of 3 only)/7 + (1/2)*(Number of multiples of both)/7Plugging in the numbers:- Multiples of 2 only: 2, 4, 8 → 3 numbers- Multiples of 3 only: 3 → 1 number- Multiples of both: 6 → 1 numberSo,- P(S) = 3/7 + (1/2)*(1/7) = 3/7 + 1/14 = (6/14 + 1/14) = 7/14 = 1/2- P(U) = 1/7 + (1/2)*(1/7) = 1/7 + 1/14 = (2/14 + 1/14) = 3/14Wait, that doesn't seem right. Let me double-check. The number of multiples of 2 is 4 (2,4,6,8), and multiples of 3 is 2 (3,6). So, the overlap is 1 (6). Therefore, multiples of 2 only are 3 (2,4,8), and multiples of 3 only are 1 (3). So, P(S) should be (3/7) + (1/2)*(1/7) = 3/7 + 1/14 = 7/14 = 1/2. Similarly, P(U) is (1/7) + (1/2)*(1/7) = 1/7 + 1/14 = 3/14.Wait, but 3/14 is approximately 0.214, and 1/2 is 0.5. That seems like a big difference. Let me think again. Maybe I made a mistake in calculating P(S). Let's see:Total probability for sweetened cereal:- Rolling a 2,4,8: 3 numbers, each with probability 1/7, so 3/7.- Rolling a 6: probability 1/7, and then choosing sweetened with probability 1/2, so (1/7)*(1/2) = 1/14.So total P(S) = 3/7 + 1/14 = (6/14 + 1/14) = 7/14 = 1/2.Similarly, for unsweetened:- Rolling a 3: probability 1/7.- Rolling a 6: probability 1/7, choosing unsweetened with probability 1/2, so 1/14.So P(U) = 1/7 + 1/14 = 3/14.Okay, that seems correct. So, each day, the probability of eating sweetened is 1/2, and unsweetened is 3/14. Therefore, the expected number of days eating sweetened is 365*(1/2) = 182.5 days, and unsweetened is 365*(3/14) ≈ 78.21 days.Wait, but the question asks for the expected value of the difference between unsweetened and sweetened. So, that would be E[U - S] = E[U] - E[S] = 78.21 - 182.5 ≈ -104.29 days.But that seems like a large negative number. Is that correct? Let me think again.Wait, maybe I made a mistake in calculating P(U). Let me recalculate:P(U) = P(rolling a multiple of 3) - P(rolling a 6 and choosing sweetened) + P(rolling a 6 and choosing unsweetened). Wait, no, that's not the right way. Actually, when rolling a 6, he chooses randomly, so half the time it's sweetened, half unsweetened. So, P(U) = P(rolling a multiple of 3 only) + (1/2)*P(rolling a 6).Similarly, P(S) = P(rolling a multiple of 2 only) + (1/2)*P(rolling a 6).So, P(S) = 3/7 + 1/14 = 7/14 = 1/2.P(U) = 1/7 + 1/14 = 3/14.Yes, that's correct. So, the expected number of days eating unsweetened is 365*(3/14) ≈ 78.21, and sweetened is 365*(1/2) = 182.5.Therefore, the difference is 78.21 - 182.5 ≈ -104.29 days. But since the question asks for the expected value of the difference between unsweetened and sweetened, it's negative, meaning he eats more sweetened cereal than unsweetened.But the problem is asking for the expected value of the difference, so it's just the expectation of U - S, which is E[U] - E[S] = (3/14 - 1/2)*365.Calculating 3/14 - 1/2 = (3/14 - 7/14) = -4/14 = -2/7.So, E[U - S] = -2/7 * 365 ≈ -104.29 days.But the problem might expect the absolute value or just the magnitude. Wait, no, it's the expected value, so it can be negative. So, the answer is approximately -104.29 days. But let's express it as an exact fraction.-2/7 * 365 = -730/7 ≈ -104.29.So, the expected value is -730/7 days, which is approximately -104.29 days.Wait, but in the initial calculation, I thought P(S) was 1/2 and P(U) was 3/14, leading to E[U - S] = (3/14 - 1/2)*365 = (-2/7)*365 = -730/7 ≈ -104.29.Yes, that seems correct. So, the expected difference is negative, meaning he eats more sweetened cereal than unsweetened by about 104.29 days.But let me think again. Is there another way to approach this? Maybe by considering the expected value per day and then multiplying by 365.Each day, the expected value of (U - S) is P(U) - P(S) = 3/14 - 1/2 = -2/7. So, over 365 days, it's -2/7 * 365 = -730/7 ≈ -104.29.Yes, that matches. So, the expected value is -730/7, which is approximately -104.29 days.But let me check if I considered the rolling again correctly. When he rolls a 1, he rolls again. So, effectively, each trial is independent, and the probability of each outcome from 2 to 8 is 1/7, as we considered earlier. So, our initial probabilities are correct.Therefore, the final answer is -730/7 days, which is approximately -104.29 days. But since the problem asks for the expected value, we can express it as an exact fraction: -730/7.Wait, but 730 divided by 7 is 104 and 2/7, so -104 2/7 days. But the problem might expect the answer in a box, so I'll write it as -730/7 or approximately -104.29.But let me check the initial probabilities again. When rolling the die, excluding 1, each number from 2 to 8 has a 1/7 chance. So, P(S) is the probability of rolling a multiple of 2, which is 4/7, but since rolling a 6 leads to a 50% chance, we have to adjust.Wait, no, actually, P(S) is the probability of eating sweetened cereal, which includes rolling a multiple of 2, and if it's 6, choosing sweetened with 50% chance. Similarly for P(U).So, P(S) = P(rolling 2,4,8) + 0.5*P(rolling 6) = 3/7 + 0.5*(1/7) = 3/7 + 1/14 = 7/14 = 1/2.Similarly, P(U) = P(rolling 3) + 0.5*P(rolling 6) = 1/7 + 1/14 = 3/14.Yes, that's correct. So, the difference per day is 3/14 - 1/2 = -2/7, leading to -730/7 over 365 days.Therefore, the expected value is -730/7 days, which is approximately -104.29 days.
❓In triangle ABC, the sides opposite to angles A, B, C are respectively a, b, c, and it satisfies frac {b}{c}= sqrt {3}sin A+cos A. (1) Find the size of angle C; (2) If c=2, find the maximum area of triangle ABC.
💡Okay, so I have this triangle ABC, and the sides opposite angles A, B, C are a, b, c respectively. The problem gives me that b/c equals sqrt(3) times sin A plus cos A. I need to find the size of angle C for part (1), and then if c is 2, find the maximum area of triangle ABC for part (2).Starting with part (1). I remember the Law of Sines, which says that a/sin A = b/sin B = c/sin C. Maybe I can use that here. The given equation is b/c = sqrt(3) sin A + cos A. If I rewrite this using the Law of Sines, since b = (c sin B)/sin C, so b/c = sin B / sin C. Therefore, sin B / sin C = sqrt(3) sin A + cos A.Hmm, so sin B = sin C (sqrt(3) sin A + cos A). But in a triangle, angles add up to pi, so B = pi - A - C. Therefore, sin B = sin(pi - A - C) = sin(A + C). So, sin(A + C) = sin C (sqrt(3) sin A + cos A).Expanding sin(A + C) using the sine addition formula: sin A cos C + cos A sin C. So, sin A cos C + cos A sin C = sin C (sqrt(3) sin A + cos A).Let me write that out:sin A cos C + cos A sin C = sqrt(3) sin A sin C + cos A sin C.Wait, I can subtract cos A sin C from both sides:sin A cos C = sqrt(3) sin A sin C.Assuming sin A is not zero, which it can't be in a triangle because angle A can't be 0 or pi. So, I can divide both sides by sin A:cos C = sqrt(3) sin C.This simplifies to tan C = 1/sqrt(3). Because tan C = sin C / cos C, so if cos C = sqrt(3) sin C, then sin C / cos C = 1/sqrt(3). So tan C = 1/sqrt(3).What angle has a tangent of 1/sqrt(3)? That's 30 degrees, or pi/6 radians. So angle C is pi/6.Okay, that seems straightforward. So for part (1), angle C is 30 degrees or pi/6 radians.Now, moving on to part (2). If c = 2, find the maximum area of triangle ABC.First, I know that the area of a triangle can be given by (1/2)ab sin C. Since C is pi/6, sin C is 1/2. So the area is (1/2)ab*(1/2) = (1/4)ab. So to maximize the area, I need to maximize ab.Given that c = 2 and angle C is pi/6, I can use the Law of Cosines to relate a, b, and c. The Law of Cosines says c^2 = a^2 + b^2 - 2ab cos C.Plugging in c = 2 and C = pi/6, cos(pi/6) is sqrt(3)/2. So:4 = a^2 + b^2 - 2ab*(sqrt(3)/2)Simplify: 4 = a^2 + b^2 - sqrt(3)ab.So, 4 = a^2 + b^2 - sqrt(3)ab.I need to maximize ab under this constraint. Hmm, how can I do this? Maybe using some inequality or optimization techniques.Let me think. Maybe I can express a^2 + b^2 in terms of ab. Let's rearrange the equation:a^2 + b^2 = 4 + sqrt(3)ab.I know that for any real numbers a and b, a^2 + b^2 >= 2ab by the AM-GM inequality. So, 4 + sqrt(3)ab >= 2ab.Let me write that:4 + sqrt(3)ab >= 2ab.Subtract sqrt(3)ab from both sides:4 >= 2ab - sqrt(3)ab.Factor out ab:4 >= ab(2 - sqrt(3)).Therefore, ab <= 4 / (2 - sqrt(3)).To make this expression nicer, I can rationalize the denominator:4 / (2 - sqrt(3)) = [4*(2 + sqrt(3))] / [(2 - sqrt(3))(2 + sqrt(3))] = [8 + 4 sqrt(3)] / (4 - 3) = 8 + 4 sqrt(3).So ab <= 8 + 4 sqrt(3). Wait, but that seems too big. Let me check my steps.Wait, when I had 4 >= ab(2 - sqrt(3)), then ab <= 4 / (2 - sqrt(3)). Then, rationalizing:Multiply numerator and denominator by (2 + sqrt(3)):4*(2 + sqrt(3)) / [(2 - sqrt(3))(2 + sqrt(3))] = (8 + 4 sqrt(3)) / (4 - 3) = 8 + 4 sqrt(3). So yes, that's correct.But wait, if ab <= 8 + 4 sqrt(3), then the maximum area is (1/4)ab <= (1/4)(8 + 4 sqrt(3)) = 2 + sqrt(3). So the maximum area is 2 + sqrt(3).But wait, is this the maximum? Because I used the inequality a^2 + b^2 >= 2ab, which becomes equality when a = b. So, the maximum ab occurs when a = b.Let me verify that. If a = b, then from the equation 4 = a^2 + a^2 - sqrt(3)a^2 = 2a^2 - sqrt(3)a^2 = a^2(2 - sqrt(3)). Therefore, a^2 = 4 / (2 - sqrt(3)) = 8 + 4 sqrt(3). So a = sqrt(8 + 4 sqrt(3)).But let me compute ab when a = b. Then ab = a^2 = 8 + 4 sqrt(3). So the area is (1/4)(8 + 4 sqrt(3)) = 2 + sqrt(3). So that's consistent.Therefore, the maximum area is 2 + sqrt(3).Wait, but let me think again. When I used the inequality a^2 + b^2 >= 2ab, I concluded that ab <= 4 / (2 - sqrt(3)). But is this the tightest bound? Because sometimes, when you have a quadratic constraint, the maximum of ab can be found using calculus or Lagrange multipliers.Alternatively, maybe I can express a in terms of b or vice versa and then find the maximum.Let me try that. From the equation:4 = a^2 + b^2 - sqrt(3)ab.Let me treat this as a quadratic in a:a^2 - sqrt(3)ab + (b^2 - 4) = 0.Using the quadratic formula, a = [sqrt(3)b ± sqrt(3b^2 - 4(b^2 - 4))]/2.Simplify the discriminant:sqrt(3b^2 - 4b^2 + 16) = sqrt(-b^2 + 16).So, for real solutions, we need -b^2 + 16 >= 0 => b^2 <= 16 => b <= 4.So, a = [sqrt(3)b ± sqrt(16 - b^2)] / 2.Now, ab = b * [sqrt(3)b ± sqrt(16 - b^2)] / 2.To maximize ab, we can consider ab as a function of b:ab = [sqrt(3)b^2 ± b sqrt(16 - b^2)] / 2.This seems complicated, but maybe taking the derivative would help. Alternatively, since I already have a bound from the earlier inequality, and it's achievable when a = b, perhaps that is indeed the maximum.Alternatively, maybe using the method of Lagrange multipliers. Let me set f(a,b) = ab, subject to the constraint g(a,b) = a^2 + b^2 - sqrt(3)ab - 4 = 0.The gradient of f is (b, a), and the gradient of g is (2a - sqrt(3)b, 2b - sqrt(3)a).Setting gradient f = lambda gradient g:b = lambda (2a - sqrt(3)b),a = lambda (2b - sqrt(3)a).From the first equation: b = 2 lambda a - sqrt(3) lambda b => b + sqrt(3) lambda b = 2 lambda a => b(1 + sqrt(3) lambda) = 2 lambda a.From the second equation: a = 2 lambda b - sqrt(3) lambda a => a + sqrt(3) lambda a = 2 lambda b => a(1 + sqrt(3) lambda) = 2 lambda b.So from both equations:b(1 + sqrt(3) lambda) = 2 lambda a,a(1 + sqrt(3) lambda) = 2 lambda b.Let me denote k = 1 + sqrt(3) lambda.Then, from first equation: b k = 2 lambda a => a = (b k)/(2 lambda).From the second equation: a k = 2 lambda b => a = (2 lambda b)/k.Therefore, (b k)/(2 lambda) = (2 lambda b)/k.Cancel b from both sides (assuming b ≠ 0, which it isn't in a triangle):k/(2 lambda) = (2 lambda)/k => k^2 = (2 lambda)^2 => k = ±2 lambda.But since k = 1 + sqrt(3) lambda, let's consider k = 2 lambda:1 + sqrt(3) lambda = 2 lambda => 1 = (2 - sqrt(3)) lambda => lambda = 1 / (2 - sqrt(3)).Rationalizing the denominator:lambda = (2 + sqrt(3)) / [(2 - sqrt(3))(2 + sqrt(3))] = (2 + sqrt(3))/1 = 2 + sqrt(3).So, lambda = 2 + sqrt(3).Then, k = 1 + sqrt(3) lambda = 1 + sqrt(3)(2 + sqrt(3)) = 1 + 2 sqrt(3) + 3 = 4 + 2 sqrt(3).From the first equation: a = (b k)/(2 lambda) = [b (4 + 2 sqrt(3))]/[2(2 + sqrt(3))].Simplify denominator: 2(2 + sqrt(3)) = 4 + 2 sqrt(3).So, a = [b (4 + 2 sqrt(3))]/[4 + 2 sqrt(3)] = b.Therefore, a = b. So the maximum occurs when a = b, which is consistent with the earlier conclusion.Thus, the maximum ab is when a = b, and then ab = (8 + 4 sqrt(3)), so the area is (1/4)(8 + 4 sqrt(3)) = 2 + sqrt(3).Therefore, the maximum area is 2 + sqrt(3).I think that's solid. I used two methods: one using the AM-GM inequality and another using Lagrange multipliers, both leading to the same conclusion that a = b gives the maximum ab, hence the maximum area.So, summarizing:(1) Angle C is pi/6 or 30 degrees.(2) The maximum area is 2 + sqrt(3).**Final Answer**(1) The size of angle ( C ) is (boxed{dfrac{pi}{6}}).(2) The maximum area of ( triangle ABC ) is (boxed{2 + sqrt{3}}).
❓If x gt -2, then the minimum value of frac{{{x^2}+6x+9}}{{x+2}} is ( )A: 1B: 2C: 3D: 4
💡Okay, so I have this problem here: If ( x > -2 ), then the minimum value of ( frac{x^2 + 6x + 9}{x + 2} ) is ( ). The options are A: 1, B: 2, C: 3, D: 4.Hmm, let's see. I need to find the minimum value of this expression when ( x ) is greater than -2. First, I should probably simplify the expression or maybe find its derivative to locate the minimum.Looking at the numerator, ( x^2 + 6x + 9 ), that looks familiar. Wait, that's a perfect square, right? Because ( (x + 3)^2 = x^2 + 6x + 9 ). So, the expression simplifies to ( frac{(x + 3)^2}{x + 2} ).Okay, so now I have ( frac{(x + 3)^2}{x + 2} ). Maybe I can rewrite this in a way that makes it easier to analyze. Let me try to expand it or manipulate it somehow.Let me consider ( (x + 3)^2 ) as ( (x + 2 + 1)^2 ). Expanding that, I get ( (x + 2)^2 + 2(x + 2) + 1 ). So, substituting back into the expression, I have:[frac{(x + 2)^2 + 2(x + 2) + 1}{x + 2}]Now, I can split this fraction into three separate terms:[frac{(x + 2)^2}{x + 2} + frac{2(x + 2)}{x + 2} + frac{1}{x + 2}]Simplifying each term:1. ( frac{(x + 2)^2}{x + 2} = x + 2 )2. ( frac{2(x + 2)}{x + 2} = 2 )3. ( frac{1}{x + 2} ) remains as it is.So, putting it all together, the expression becomes:[x + 2 + 2 + frac{1}{x + 2} = x + 4 + frac{1}{x + 2}]Wait, that's not quite right. Let me check my steps again. When I split the fraction, it should be:[frac{(x + 2)^2}{x + 2} + frac{2(x + 2)}{x + 2} + frac{1}{x + 2} = (x + 2) + 2 + frac{1}{x + 2}]So, combining the constants:[(x + 2) + 2 + frac{1}{x + 2} = x + 4 + frac{1}{x + 2}]Wait, no, that's not correct. Let me recast it properly. The first term is ( x + 2 ), the second term is 2, and the third term is ( frac{1}{x + 2} ). So, adding them together:[(x + 2) + 2 + frac{1}{x + 2} = x + 4 + frac{1}{x + 2}]Hmm, that seems a bit off. Let me think differently. Maybe instead of expanding, I should consider substitution to simplify the expression.Let me let ( t = x + 2 ). Since ( x > -2 ), then ( t > 0 ). So, substituting ( x = t - 2 ) into the expression:[frac{(t - 2)^2 + 6(t - 2) + 9}{t}]Let me compute the numerator:[(t - 2)^2 = t^2 - 4t + 4][6(t - 2) = 6t - 12]Adding these together with 9:[t^2 - 4t + 4 + 6t - 12 + 9 = t^2 + 2t + 1]So, the expression becomes:[frac{t^2 + 2t + 1}{t} = frac{(t + 1)^2}{t}]That's better. Now, I have ( frac{(t + 1)^2}{t} ) where ( t > 0 ). I need to find the minimum value of this expression.Let me expand the numerator:[(t + 1)^2 = t^2 + 2t + 1]So, the expression is:[frac{t^2 + 2t + 1}{t} = frac{t^2}{t} + frac{2t}{t} + frac{1}{t} = t + 2 + frac{1}{t}]Okay, so now the expression is ( t + 2 + frac{1}{t} ). I need to find its minimum for ( t > 0 ).This looks like a function where I can apply the AM-GM inequality. The AM-GM inequality states that for positive real numbers, the arithmetic mean is greater than or equal to the geometric mean. Specifically, for two positive numbers ( a ) and ( b ):[frac{a + b}{2} geq sqrt{ab}]Equality holds when ( a = b ).In this case, I have ( t ) and ( frac{1}{t} ). Let me apply AM-GM to these two terms:[frac{t + frac{1}{t}}{2} geq sqrt{t cdot frac{1}{t}} = sqrt{1} = 1]Multiplying both sides by 2:[t + frac{1}{t} geq 2]So, the minimum value of ( t + frac{1}{t} ) is 2, achieved when ( t = frac{1}{t} ), which implies ( t = 1 ).Therefore, the expression ( t + 2 + frac{1}{t} ) has a minimum value of ( 2 + 2 = 4 ).Wait, hold on. Let me double-check that. If ( t + frac{1}{t} geq 2 ), then adding 2 to both sides gives:[t + 2 + frac{1}{t} geq 4]Yes, that's correct. So, the minimum value of the expression is 4, achieved when ( t = 1 ).Since ( t = x + 2 ), setting ( t = 1 ) gives ( x + 2 = 1 ), so ( x = -1 ).Let me verify this by plugging ( x = -1 ) back into the original expression:[frac{(-1)^2 + 6(-1) + 9}{-1 + 2} = frac{1 - 6 + 9}{1} = frac{4}{1} = 4]Yes, that checks out. So, the minimum value is indeed 4.Alternatively, I could have used calculus to find the minimum. Let me try that approach as well to confirm.Starting with the expression ( f(x) = frac{x^2 + 6x + 9}{x + 2} ). To find the minimum, I can take the derivative and set it equal to zero.First, let's find ( f'(x) ). Using the quotient rule:[f'(x) = frac{(2x + 6)(x + 2) - (x^2 + 6x + 9)(1)}{(x + 2)^2}]Simplify the numerator:[(2x + 6)(x + 2) = 2x(x) + 2x(2) + 6(x) + 6(2) = 2x^2 + 4x + 6x + 12 = 2x^2 + 10x + 12][(x^2 + 6x + 9)(1) = x^2 + 6x + 9]Subtracting the second expression from the first:[2x^2 + 10x + 12 - (x^2 + 6x + 9) = x^2 + 4x + 3]So, the derivative is:[f'(x) = frac{x^2 + 4x + 3}{(x + 2)^2}]To find critical points, set ( f'(x) = 0 ):[x^2 + 4x + 3 = 0]Solving the quadratic equation:[x = frac{-4 pm sqrt{16 - 12}}{2} = frac{-4 pm 2}{2}]So, ( x = frac{-4 + 2}{2} = -1 ) or ( x = frac{-4 - 2}{2} = -3 ).But since ( x > -2 ), ( x = -3 ) is not in the domain. So, the only critical point is at ( x = -1 ).To confirm if this is a minimum, I can check the second derivative or analyze the behavior around ( x = -1 ).Alternatively, since we already found using AM-GM that the minimum is 4 at ( x = -1 ), and the derivative approach also leads us to ( x = -1 ) as the critical point, it's safe to conclude that the minimum value is indeed 4.So, the answer should be D: 4.
❓Define a function g(x), for positive integer values of x, by:[ g(x) = left{begin{aligned}log_{16} x & quad text{if } log_{16} x text{ is an integer} 2 + g(x - 1) & quad text{otherwise}.end{aligned}right. ]Compute g(256).
💡Okay, so I have this function g(x) defined for positive integers x. It has two cases: if log base 16 of x is an integer, then g(x) is just that log value. Otherwise, g(x) is 2 plus g(x-1). I need to compute g(256). Hmm, let's break this down step by step.First, let me recall what log base 16 means. The logarithm log_{16} x is the exponent you need to raise 16 to, to get x. So, for example, log_{16} 16 is 1 because 16^1 = 16, and log_{16} 256 is 2 because 16^2 = 256. So, if x is a power of 16, then log_{16} x is an integer, and that's the value of g(x). Otherwise, I have to subtract 1 from x and add 2 to the result of g(x-1).So, let's start with g(256). Is 256 a power of 16? Well, 16 squared is 256, so yes, log_{16} 256 is 2. Therefore, according to the first case, g(256) should be 2. But wait, let me make sure I'm not missing something here.Wait, the function is defined recursively. So, if I use the first case, it's straightforward, but maybe I need to check if the second case applies? Let me think. The function says if log_{16} x is an integer, use that; otherwise, use 2 + g(x-1). Since log_{16} 256 is 2, which is an integer, we don't need to use the second case. So, g(256) is just 2. Is that all?But wait, in the initial problem statement, the user provided a thought process where they started applying the second case, subtracting 1 each time and adding 2, but then realized that 256 is a power of 16 and concluded g(256) is 2. So, maybe I should verify this by stepping through the recursion.Let me try computing g(256) using the second case just to see what happens. So, if I don't recognize that 256 is a power of 16, I might start with g(256) = 2 + g(255). Then, g(255) would be 2 + g(254), and so on, all the way down. But that seems like it would take a lot of steps, and I might end up in an infinite loop if I'm not careful.Wait, but actually, since 256 is a power of 16, when we get down to x=256, we can stop the recursion because log_{16} 256 is an integer. So, if I were to write out the recursion, it would be:g(256) = 2 + g(255)g(255) = 2 + g(254)...g(16) = 2 + g(15)g(15) = 2 + g(14)...g(1) = ?Wait, hold on, what is g(1)? Because if x=1, log_{16} 1 is 0, which is an integer, so g(1) = 0. So, if I were to compute g(256) by subtracting 1 each time, I would have to add 2 each time until I reach x=1, which would give me g(1)=0. Then, the total would be 2*(256-1) + 0 = 2*255 = 510. But that contradicts the initial thought that g(256)=2.Hmm, so which one is correct? Is g(256)=2 or 510? I think I need to clarify the function's definition. The function says if log_{16} x is an integer, then g(x)=log_{16} x. Otherwise, g(x)=2 + g(x-1). So, for x=256, since log_{16} 256=2 is an integer, we use the first case, so g(256)=2. The second case only applies when log_{16} x is not an integer, which is not the case here.Therefore, the correct answer should be 2. The initial thought process that led to 510 was incorrect because it didn't recognize that x=256 is a power of 16 and thus should use the first case directly. So, I think the correct answer is 2.But just to make sure, let me test this with a smaller number. Let's say x=16. Then, log_{16} 16=1, so g(16)=1. If I try to compute it using the second case, I would get g(16)=2 + g(15). Then, g(15)=2 + g(14), and so on, until g(1)=0. So, g(16)=2*15 + 0=30, which is not correct because g(16) should be 1. So, this shows that when x is a power of 16, we must use the first case and not the second case.Therefore, for x=256, which is 16^2, log_{16} 256=2, so g(256)=2. The recursion only applies when x is not a power of 16. So, the correct answer is 2.I think I confused myself earlier by trying to apply the second case when the first case already applies. It's important to check if x is a power of 16 before applying the recursive step. So, in conclusion, g(256)=2.
❓Consider two circles with different radii, r1 and r2, and a square with an area of 784 sq cm. The side of the square is twice the radius of the larger circle, and its diagonal is equal to the sum of the radii of both circles. The radius of the larger circle is seven-thirds that of the smaller circle. Furthermore, let there be an isosceles right triangle with hypotenuse equal to the diagonal of the square and one leg passing through the center of the smaller circle. The length of this leg is equal to the difference between the radius of the smaller circle and half of the side of the square. Using the given information, form a system of algebraic equations involving the circle radii, square side length, and triangle leg lengths, and solve for the circumference of the smaller circle.
💡Alright, so I've got this problem here about two circles and a square, and I need to find the circumference of the smaller circle. Let me try to unpack all the information step by step.First, there are two circles with different radii, r1 and r2. I guess r1 is the smaller one and r2 is the larger one. Then there's a square with an area of 784 square centimeters. Okay, so the area of a square is side length squared, so if I let s be the side length, then s squared equals 784. That means s is the square root of 784, which is 28 cm. Got that.Next, it says the side of the square is twice the radius of the larger circle. So, s = 2 * r2. Since I already found s is 28 cm, that means 28 = 2 * r2, so r2 must be 14 cm. Okay, so the larger circle has a radius of 14 cm.Then, it mentions that the diagonal of the square is equal to the sum of the radii of both circles. The diagonal of a square can be found using the formula s * sqrt(2). So, the diagonal d = 28 * sqrt(2). But this diagonal is also equal to r1 + r2. I already know r2 is 14 cm, so I can write 28 * sqrt(2) = r1 + 14. Hmm, that seems a bit complicated because sqrt(2) is an irrational number, but maybe it will cancel out later.Wait, there's more information. It says the radius of the larger circle is seven-thirds that of the smaller circle. So, r2 = (7/3) * r1. Since r2 is 14 cm, I can set up the equation 14 = (7/3) * r1. Solving for r1, I multiply both sides by 3/7, so r1 = 14 * (3/7) = 6 cm. Okay, so the smaller circle has a radius of 6 cm.Now, moving on to the isosceles right triangle part. The hypotenuse of this triangle is equal to the diagonal of the square, which we already found to be 28 * sqrt(2). In an isosceles right triangle, the legs are equal, and the hypotenuse is leg * sqrt(2). So, if the hypotenuse is 28 * sqrt(2), then each leg must be 28 cm because 28 * sqrt(2) divided by sqrt(2) is 28.But wait, there's another condition. One leg of the triangle passes through the center of the smaller circle, and the length of this leg is equal to the difference between the radius of the smaller circle and half of the side of the square. So, the leg length l = r1 - (s/2). Plugging in the numbers, l = 6 - (28/2) = 6 - 14 = -8 cm. Wait, that doesn't make sense because length can't be negative. Did I do something wrong?Let me check. The leg length is supposed to be equal to the difference between the radius of the smaller circle and half of the side of the square. So, l = r1 - (s/2). If r1 is 6 and s is 28, then s/2 is 14, so 6 - 14 is indeed -8. That's negative, which doesn't make sense for a length. Maybe I misinterpreted the condition.Perhaps it's the absolute difference? Or maybe the order is reversed? Let me read it again: "The length of this leg is equal to the difference between the radius of the smaller circle and half of the side of the square." So, it's r1 - (s/2). But since s/2 is larger than r1, it's negative. Maybe it's the other way around? Maybe it's (s/2) - r1? That would make sense because 14 - 6 = 8 cm, which is positive. But the problem says "the difference between the radius of the smaller circle and half of the side of the square," which is r1 - (s/2). Hmm, maybe I need to take the absolute value.But in any case, the leg length we calculated earlier from the hypotenuse was 28 cm, and this condition gives us either -8 or 8 cm, depending on the interpretation. There's a discrepancy here. Maybe I made a mistake earlier.Let me go back. The diagonal of the square is 28 * sqrt(2), which is approximately 39.6 cm. The sum of the radii is r1 + r2 = 6 + 14 = 20 cm. Wait, that doesn't match the diagonal. 20 cm is much less than 39.6 cm. So, there's a problem here.Wait, the diagonal of the square is equal to the sum of the radii? That can't be right because the diagonal is much longer than the sum of the radii. Did I misinterpret the relationship? Let me check the problem again.It says, "the diagonal is equal to the sum of the radii of both circles." So, d = r1 + r2. But d is 28 * sqrt(2), which is about 39.6 cm, and r1 + r2 is 20 cm. That's not equal. So, something's wrong here.Maybe I made a mistake in calculating the diagonal. Wait, the diagonal of the square is s * sqrt(2), which is 28 * sqrt(2). That's correct. So, if d = r1 + r2, then r1 + r2 = 28 * sqrt(2). But earlier, I found r2 = 14 cm, so r1 = 28 * sqrt(2) - 14. That would make r1 approximately 28 * 1.414 - 14 ≈ 39.6 - 14 = 25.6 cm. But that contradicts the earlier statement that r2 is seven-thirds of r1. If r1 is 25.6, then r2 would be (7/3)*25.6 ≈ 59.7 cm, which is much larger than 14 cm. So, there's a conflict here.I think I need to re-examine the relationships. Let's list out all the given information:1. Area of square = 784 cm² → side s = 28 cm.2. s = 2 * r2 → r2 = 14 cm.3. Diagonal of square = r1 + r2 → 28 * sqrt(2) = r1 + 14.4. r2 = (7/3) * r1 → 14 = (7/3) * r1 → r1 = 6 cm.5. Isosceles right triangle with hypotenuse = diagonal of square = 28 * sqrt(2).6. One leg of the triangle passes through the center of the smaller circle, and its length is equal to r1 - (s/2) = 6 - 14 = -8 cm.From point 3, if 28 * sqrt(2) = r1 + 14, then r1 = 28 * sqrt(2) - 14 ≈ 25.6 cm. But from point 4, r1 = 6 cm. These two results for r1 are conflicting. That means there's an inconsistency in the problem or my interpretation.Wait, maybe the diagonal of the square is not equal to r1 + r2, but something else. Let me read the problem again carefully."The side of the square is twice the radius of the larger circle, and its diagonal is equal to the sum of the radii of both circles."So, s = 2 * r2 and d = r1 + r2.Given that, s = 28 cm, so r2 = 14 cm.Then, d = 28 * sqrt(2) = r1 + 14 → r1 = 28 * sqrt(2) - 14 ≈ 25.6 cm.But also, r2 = (7/3) * r1 → 14 = (7/3) * r1 → r1 = 6 cm.So, r1 cannot be both 25.6 cm and 6 cm. There's a contradiction here. That suggests that either the problem has conflicting information or I'm misapplying the relationships.Perhaps the diagonal is not equal to the sum of the radii, but the sum of the radii equals the diagonal? Wait, that's what it says: "its diagonal is equal to the sum of the radii of both circles." So, d = r1 + r2.But with s = 28 cm, d = 28 * sqrt(2) ≈ 39.6 cm, and r1 + r2 = 6 + 14 = 20 cm. They are not equal. So, something's wrong.Maybe the problem meant that the sum of the radii equals the side of the square? Let me check: "the diagonal is equal to the sum of the radii of both circles." No, it's the diagonal.Alternatively, perhaps the diagonal is equal to the difference of the radii? Or maybe the sum of the diameters? Let me see.If it's the sum of the diameters, then d = 2r1 + 2r2 = 2(r1 + r2). Then, 28 * sqrt(2) = 2(r1 + r2) → r1 + r2 = 14 * sqrt(2) ≈ 19.8 cm. But from r2 = (7/3)r1, r1 + (7/3)r1 = (10/3)r1 = 14 * sqrt(2) → r1 = (14 * sqrt(2)) * (3/10) ≈ (19.8) * 0.3 ≈ 5.94 cm, which is approximately 6 cm. That matches the earlier result from r2 = (7/3)r1.So, maybe the problem meant the diagonal is equal to the sum of the diameters, not the radii. That would make sense because then the numbers align. Let me assume that for a moment.If d = 2r1 + 2r2 = 2(r1 + r2), then:28 * sqrt(2) = 2(r1 + r2) → r1 + r2 = 14 * sqrt(2).Given that r2 = (7/3)r1, then:r1 + (7/3)r1 = (10/3)r1 = 14 * sqrt(2) → r1 = (14 * sqrt(2)) * (3/10) = (42 * sqrt(2))/10 ≈ (42 * 1.414)/10 ≈ 59.388/10 ≈ 5.938 cm, which is approximately 6 cm. That matches the earlier result.So, perhaps there was a misstatement in the problem, and it should be the sum of the diameters instead of the radii. Alternatively, maybe I need to consider that the diagonal is equal to the sum of the radii, but that leads to inconsistency.Given the contradiction, I think the intended relationship is that the diagonal equals the sum of the diameters. So, proceeding with that assumption:r1 + r2 = 14 * sqrt(2).But since r2 = (7/3)r1, then:r1 + (7/3)r1 = (10/3)r1 = 14 * sqrt(2) → r1 = (14 * sqrt(2)) * (3/10) = (42 * sqrt(2))/10 ≈ 5.938 cm.But earlier, from s = 2r2, we have r2 = 14 cm, which would make r1 = (3/7)*14 = 6 cm. So, r1 is 6 cm, and r2 is 14 cm.Now, checking the diagonal:d = 28 * sqrt(2) ≈ 39.6 cm.Sum of radii: 6 + 14 = 20 cm.Sum of diameters: 12 + 28 = 40 cm, which is close to 39.6 cm, considering rounding.So, perhaps the problem intended the diagonal to be equal to the sum of the diameters, which would make sense because then the numbers almost match.Assuming that, then r1 = 6 cm, and the circumference is 2 * pi * r1 = 12 pi cm.But going back to the isosceles right triangle part:Hypotenuse = diagonal of square = 28 * sqrt(2).Leg length = r1 - (s/2) = 6 - 14 = -8 cm. Again, negative.Alternatively, if it's (s/2) - r1 = 14 - 6 = 8 cm.In an isosceles right triangle, the legs are equal, and hypotenuse = leg * sqrt(2). So, if leg = 8 cm, then hypotenuse = 8 * sqrt(2) ≈ 11.31 cm, which is much less than the diagonal of the square, which is 28 * sqrt(2) ≈ 39.6 cm. So, that doesn't match.Alternatively, if the leg is 28 cm, then hypotenuse = 28 * sqrt(2), which matches the diagonal. But then the leg length is 28 cm, which is equal to s, the side of the square.But according to the problem, the leg length is equal to r1 - (s/2) = 6 - 14 = -8 cm, which is negative. So, there's a conflict.Perhaps the leg length is the absolute value, so 8 cm. Then, hypotenuse would be 8 * sqrt(2) ≈ 11.31 cm, which doesn't match the diagonal.Alternatively, maybe the leg length is (s/2) - r1 = 14 - 6 = 8 cm, and the hypotenuse is 8 * sqrt(2), but that's still not matching the diagonal.This suggests that there's an inconsistency in the problem as stated. The relationships provided lead to conflicting results.However, assuming that the diagonal is equal to the sum of the radii, despite the inconsistency, and proceeding with r1 = 6 cm, then the circumference is 12 pi cm.Alternatively, if the diagonal is equal to the sum of the diameters, then r1 ≈ 5.938 cm, and circumference ≈ 37.3 cm, but that doesn't align with the integer values given in the problem.Given the problem's context and the integer values, I think the intended solution is to take r1 = 6 cm, circumference = 12 pi cm, despite the inconsistency with the diagonal.So, final answer: 12 pi cm.