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Let f: (0, infty) to mathbfR be a twice differentiable function. If for some a neq 0 , int_0^1 f(lambda x) \, mathrmdlambda = a f(x) , f(1) = 1 and f(16) = frac18 , then 16 - f'(frac116) is equal to

Numerical Answer Type:
Enter a numerical value Answer: 112 +4 marks

Solution & Explanation

### Related Formula textLeibniz Integral Rule for differentiation: fracddxint_0^x f(t) \, dt = f(x) ### Core Logic Perform variable substitution inside the integral: let lambda x = t implies dlambda = frac1x dt. When lambda = 0 implies t = 0; when lambda = 1 implies t = x. The equation transforms to: frac1x int_0^x f(t) \, dt = a f(x) implies int_0^x f(t) \, dt = a x f(x) ### Step 1: Differentiate with respect to x Using Leibniz rule and product rule: f(x) = a [x f'(x) + f(x)] (1 - a)f(x) = a x f'(x) implies fracf'(x)f(x) = frac1-aa frac1x Integrating both sides yields: ln f(x) = left(frac1-aaright)ln x + c implies f(x) = C x^frac1-aa ### Step 2: Calculate Constants using boundaries Given f(1) = 1 implies C = 1. Given f(16) = frac18 implies frac18 = (16)^frac1-aa implies 2^-3 = (2^4)^frac1-aa -3 = frac4(1-a)a implies -3a = 4 - 4a implies a = 4 Therefore, power exponent = frac1-44 = -frac34 implies f(x) = x^-frac34. ### Step 3: Evaluate target derivative value Find the derivative: f'(x) = -frac34 x^-frac74 Substitute x = frac116: f'left(frac116right) = -frac34 left(2^-4right)^-frac74 = -frac34 left(2^7right) = -frac34 times 128 = -96 Final requested computation calculation: 16 - f'left(frac116right) = 16 - (-96) = 112 ### Pattern Recognition Scaling inputs inside functional definite integrals tracks closely to homogenous Euler equation properties. Converting integrations quickly to local power functions reduces processing parameters. ### Evaluation Rubric / Model Answer null ### Chapter Mix Class 12 Mathematics: Definite Integrals Class 12 Mathematics: Differential Equations

Reference Study Guides

More Definite Integrals Previous-Year Questions — Page 2

Q52 2025 Properties of Definite Integrals
If I(m,n) = int_0^1 x^m-1 (1-x)^n-1 dx where m, n > 0, then I(9,14) + I(10,13) is :
  • A. I(9, 1)
  • B. I(19, 27)
  • C. I(1, 13)
  • D. I(9, 13)

Solution

### Related Formula The beta function integral format satisfies: I(m,n) = int_0^1 x^m-1 (1-x)^n-1 dx ### Core Logic Let's combine the terms of the requested sum directly by inserting their respective definitions: I(9,14) = int_0^1 x^9-1 (1-x)^14-1 dx = int_0^1 x^8 (1-x)^13 dx I(10,13) = int_0^1 x^10-1 (1-x)^13-1 dx = int_0^1 x^9 (1-x)^12 dx ### Step 1: Factoring out common algebraic terms Summing the two components: I(9,14) + I(10,13) = int_0^1 left[ x^8 (1-x)^13 + x^9 (1-x)^12 right] dx Factor out the common term x^8 (1-x)^12 inside the integrand: = int_0^1 x^8 (1-x)^12 left[ (1-x) + x right] dx = int_0^1 x^8 (1-x)^12 (1) dx = int_0^1 x^9-1 (1-x)^13-1 dx = I(9,13) ### Pattern Recognition When dealing with linear combinations of beta functions with shifting parameter indices, directly writing down the definite integral expression often results in immediate algebraic cancellation or simplification via basic factoring. ### Evaluation Rubric / Model Answer null ### Chapter Mix Class 12 Mathematics: Definite Integrals
Q71 2025 Differentiating Under the Integral Sign
Let f be a differentiable function such that 2(x+2)^2f(x) - 3(x+2)^2 = 10int_0^x(t+2)f(t)dt for x geq 0. Then f(2) is equal to ________.
Numerical Answer. Answer: 19

Solution

### Related Formula The Leibniz Integral Rule template allows direct differentiation of an integral with variable limits: fracddxleft( int_0^x g(t) dt right) = g(x) ### Core Logic Differentiate both sides of the given functional equation with respect to x using the product rule: fracddxleft[ 2(x+2)^2 f(x) - 3(x+2)^2 right] = fracddxleft[ 10int_0^x(t+2)f(t)dt right] 4(x+2)f(x) + 2(x+2)^2 f'(x) - 6(x+2) = 10(x+2)f(x) Since x geq 0, the factor (x+2) is strictly non-zero. Divide the entire equation by 2(x+2): 2f(x) + (x+2)f'(x) - 3 = 5f(x) (x+2)f'(x) - 3f(x) = 3 ### Step 1: Solve the First-Order Differential Equation Rearrange the expression into standard linear differential equation form where y = f(x): fracdydx - frac3x+2y = frac3x+2 Compute the Integrating Factor (I.F.): textI.F. = e^int -frac3x+2 dx = e^-3ln(x+2) = (x+2)^-3 Multiply through by the I.F. and integrate: y cdot (x+2)^-3 = int frac3x+2 cdot (x+2)^-3 dx = int 3(x+2)^-4 dx fracf(x)(x+2)^3 = 3 cdot frac(x+2)^-3-3 + C = -(x+2)^-3 + C f(x) = -1 + C(x+2)^3 ### Step 2: Apply the Boundary Condition Find the boundary condition by substituting x = 0 into the original integral equation equation: 2(0+2)^2 f(0) - 3(0+2)^2 = 10 int_0^0 (t+2)f(t) dt 8f(0) - 12 = 0 implies f(0) = frac128 = frac32 Substitute x = 0 into our general solution formula: f(0) = -1 + C(0+2)^3 implies frac32 = -1 + 8C frac52 = 8C implies C = frac516 Thus, the explicit function is: f(x) = -1 + frac516(x+2)^3 ### Step 3: Evaluate at target point x = 2 Substitute x = 2 into the final function equation: f(2) = -1 + frac516(2+2)^3 = -1 + frac516(64) f(2) = -1 + 5(4) = -1 + 20 = 19 ### Pattern Recognition When an equation contains a variable integral limit int_0^x, differentiating both sides using the Leibniz rule converts it into a standard differential equation. The initial value is found by setting x = 0 directly in the original expression. ### Evaluation Rubric / Model Answer null ### Chapter Mix Class 12 Mathematics: Definite Integrals Class 12 Mathematics: Differential Equations
Q66 2025 Integration by Substitution
The integral 80int_0^fracpi4left(fracsintheta + costheta9 + 16sin 2thetaright)mathrmdtheta is equal to:
  • A. 3log_e4
  • B. 6log_mathrme4
  • C. 4log_mathrme3
  • D. 2log_e3

Solution

### Related Formula int fracdta^2 - b^2 t^2 = frac12a ln left| fraca+bta-bt right| sin 2theta = 1 - (sintheta - costheta)^2 ### Core Logic Let sintheta - costheta = t. Then (costheta + sintheta)dtheta = dt. Transform limits: When theta = 0 implies t = 0 - 1 = -1 When theta = fracpi4 implies t = frac1sqrt2 - frac1sqrt2 = 0 ### Step 1: Perform the algebraic substitution Express the denominator base: 9 + 16sin 2theta = 9 + 16[1 - t^2] = 25 - 16t^2 The integral transforms to: I = 80 int_-1^0 fracdt25 - 16t^2 = frac8016 int_-1^0 fracdtleft(frac54right)^2 - t^2 ### Step 2: Execute Integral Calculation I = 5 left[ frac12left(frac54right) ln left| fracfrac54 + tfrac54 - t right| right]_-1^0 I = 2 left[ ln(1) - lnleft( frac1/49/4 right) right] = 2 left[ 0 - lnleft(frac19right) right] = 2ln(9) = 4ln(3) ### Pattern Recognition Whenever (sintheta + costheta) sits inside the numerator, instantly choose t = sintheta - costheta as your core linear substitution engine to clean denominators. ### Evaluation Rubric / Model Answer null ### Chapter Mix Class 12 Mathematics: Definite Integrals

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