Let f be a differentiable function such that 2(x+2)²f(x) - 3(x+2)² = 10∫₀x(t+2)f(t)dt for x ≥ 0. Then f(2) is equal to ________.

Numerical Answer Type:
Enter a numerical value Answer: 19 +4 marks

Solution & Explanation

Related Formula

The Leibniz Integral Rule template allows direct differentiation of an integral with variable limits:

(d)/(dx)( ∫₀x g(t) dt ) = g(x)
Core Logic

Differentiate both sides of the given functional equation with respect to x using the product rule:

(d)/(dx)[ 2(x+2)² f(x) - 3(x+2)² ] = (d)/(dx)[ 10∫₀x(t+2)f(t)dt ] 4(x+2)f(x) + 2(x+2)² f'(x) - 6(x+2) = 10(x+2)f(x)

Since x ≥ 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):

(dy)/(dx) - (3)/(x+2)y = (3)/(x+2)

Compute the Integrating Factor (I.F.):

I.F. = e∫ -(3)/(x+2) dx = e-3ln(x+2) = (x+2)⁻³

Multiply through by the I.F. and integrate:

y · (x+2)⁻³ = ∫ (3)/(x+2) · (x+2)⁻³ dx = ∫ 3(x+2)⁻⁴ dx (f(x))/((x+2)³) = 3 · (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 ∫₀⁰ (t+2)f(t) dt 8f(0) - 12 = 0 f(0) = (12)/(8) = (3)/(2)

Substitute x = 0 into our general solution formula:

f(0) = -1 + C(0+2)³ (3)/(2) = -1 + 8C (5)/(2) = 8C C = (5)/(16)

Thus, the explicit function is:

f(x) = -1 + (5)/(16)(x+2)³
Step 3: Evaluate at target point x = 2

Substitute x = 2 into the final function equation:

f(2) = -1 + (5)/(16)(2+2)³ = -1 + (5)/(16)(64) f(2) = -1 + 5(4) = -1 + 20 = 19
Pattern Recognition

When an equation contains a variable integral limit ∫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.

Chapter Mix

Class 12 Mathematics: Definite Integrals Class 12 Mathematics: Differential Equations

Reference Study Guides

More Definite Integrals Previous-Year Questions

Q12 jee_main_2026_21_jan_morning Properties of Definite Integrals with Modulus
The value of ∫-π/6π/6( π+4x¹¹1- (|x|+π/6))dx is equal to
  • A. 2π
  • B. 4π
  • C. 8π
  • D. 6π

Solution

Related Formula
∫₋ₐa f(x) dx = ∫₀a [f(x) + f(-x)] dx
Core Logic

Let I = ∫-π/6π/6 π+4x¹¹1- (|x|+π/6)dx. The denominator 1 - (|x| + π/6) is an even function. The numerator can be split into an even part (π) and an odd part (4x¹¹).

∫₋ₐa 4x¹¹1- (|x|+π/6) dx = 0 (Since integrand is odd)
Step 1: Simplify to Even Integral

We are left with the even part:

I = ∫-π/6π/6 (π)/(1 - (|x| + π/6)) dx

Using even function property ∫₋ₐa f(x) dx = 2 ∫₀a f(x) dx:

I = 2π ∫₀π/6 (1)/(1 - (x + π/6)) dx
Step 2: Substitution

Let t = x + (π)/(6) ⇒ dt = dx. Limits: when x = 0 ⇒ t = π/6, when x = π/6 ⇒ t = π/3.

I = 2π ∫π/6π/3 (dt)/(1 - t)
Step 3: Solve the Integral

Rationalize the denominator:

I = 2π ∫π/6π/3 (1 + t)/((1 - t)(1 + t)) dt I = 2π ∫π/6π/3 (1 + t)/( ² t) dt I = 2π ∫π/6π/3 ( ² t + t t) dt

Integrate directly:

I = 2π [ t + t ]π/6π/3

Evaluate limits: Upper limit (π/3): (π/3) + (π/3) = √(3) + 2 Lower limit (π/6): (π/6) + (π/6) = 1√(3) + 2√(3) = 3√(3) = √(3)

I = 2π [(√(3) + 2) - √(3)] = 2π (2) = 4π
Pattern Recognition

Symmetric limits [-a, a] instantly demand testing for odd/even parity. Any mixed polynomial like c + k xodd over an even denominator guarantees the odd power term strictly vanishes, halving calculation time.

Chapter Mix

Class 12 Maths: Definite Integration Class 11 Maths: Trigonometric Functions

Q25 jee_main_2026_21_jan_morning Absolute Value Integrals
6∫₀π|( 3x+ 2x+ x)|dx is equal to.....
Numerical Answer. Answer: 17 to 17

Solution

Related Formula
A + B = 2 ((A+B)/(2)) ((A-B)/(2)) 2x = 2 x x 2x = 2 ² x - 1
Core Logic

Let I = 6∫₀π| 3x + x + 2x| dx. Apply sum-to-product on 3x + x: 3x + x = 2 (2x) (x)

So the expression becomes: |2 (2x) x + 2x| = | 2x (2 x + 1)| = |2 x x (2 x + 1)| Since x in [0, π], x ≥ 0. We can pull it out of the modulus. I = 12 ∫₀π x |2 ² x + x| dx

Step 1: Coordinate Substitution

Substitute t = x, then dt = - x dx. Limits: when x = 0, t = 1. When x = π, t = -1.

I = 12 ∫₋₁¹ |2t² + t| dt
Step 2: Resolve Modulus Intervals

The roots of 2t² + t = 0 are t = 0 and t = -1/2. The quadratic 2t² + t is negative in the interval (-1/2, 0) and positive elsewhere. Split the integral:

I = 12 [ ∫₋₁-1/2 (2t² + t) dt - ∫-1/2⁰ (2t² + t) dt + ∫₀¹ (2t² + t) dt ]

Integration of modulus polynomial function diagram for Q25 - JEE Main 2026 Morning
Integration of modulus polynomial function diagram for Q25 - JEE Main 2026 Morning

Step 3: Evaluate Integrals

Anti-derivative: F(t) = (2t³)/(3) + (t²)/(2). F(1) = 2/3 + 1/2 = 7/6 F(0) = 0 F(-1/2) = 2(-1/8)/3 + 1/8 = -1/12 + 1/8 = 1/24 F(-1) = -2/3 + 1/2 = -1/6

Evaluate each segment:

  • ∫₋₁-1/2 = F(-1/2) - F(-1) = 1/24 - (-1/6) = 1/24 + 4/24 = 5/24
  • -∫-1/2⁰ = -(F(0) - F(-1/2)) = -(0 - 1/24) = 1/24
  • ∫₀¹ = F(1) - F(0) = 7/6 - 0 = 28/24
  • Sum of parts inside bracket: (5)/(24) + (1)/(24) + (28)/(24) = (34)/(24) = (17)/(12)

Step 4: Final Output
I = 12 × (17)/(12) = 17
Pattern Recognition

Whenever an integral features a cascading sum of sine frequencies like (kx), pair the highest and lowest frequencies first. The resulting common factor often matches the middle term, instantly yielding a clean polynomial substitution under t = x.

Chapter Mix

Class 12 Maths: Definite Integration Class 11 Maths: Trigonometric Functions

Q22 jee_main_2026_21_jan_evening Properties of Definite Integrals
If ∫₀¹4 ⁻¹(1-2x+4x²)dx=a ⁻¹(2)-b ₑ(5), where a, b in N, then (2a+b) is equal to ____.
Numerical Answer. Answer: 9 to 9

Solution

Related Formula
⁻¹(y) = ⁻¹((1)/(y)) ⁻¹((x - y)/(1 + xy)) = ⁻¹x - ⁻¹y King's Property: ∫₀^a f(x)dx = ∫₀^a f(a-x)dx
Core Logic

Let I = ∫₀¹ ⁻¹(1-2x+4x²) dx. Convert ⁻¹ to ⁻¹:

⁻¹(1 + 2x(2x-1)) = ⁻¹( (1)/(1 + 2x(2x-1)) )

Notice that 2x - (2x-1) = 1. Thus, the integrand is ⁻¹( (2x - (2x-1))/(1 + 2x(2x-1)) ).

I = ∫₀¹ ( ⁻¹(2x) - ⁻¹(2x-1) ) dx
Step 1: Apply Definite Integral Properties

Applying King's property to the second term ∫₀¹ ⁻¹(2x-1) dx:

x → 1-x ∫₀¹ ⁻¹(2(1-x)-1) dx = ∫₀¹ ⁻¹(1-2x) dx = -∫₀¹ ⁻¹(2x-1) dx

Wait, this implies ∫₀¹ ⁻¹(2x-1) dx = 0! Thus, I = ∫₀¹ ⁻¹(2x) dx.

Step 2: Integration by Parts

Solve ∫₀¹ ⁻¹(2x) · 1 dx:

I = [ x ⁻¹(2x) ]₀¹ - ∫₀¹ x (2)/(1+4x²) dx I = ⁻¹(2) - (1)/(4) ∫₀¹ (8x)/(1+4x²) dx

Let 1+4x² = t 8x dx = dt. At x=0, t=1; at x=1, t=5.

I = ⁻¹(2) - (1)/(4) ∫₁⁵ (dt)/(t) = ⁻¹(2) - (1)/(4) ln(5)
Step 3: Compare and Calculate Result

The original integral has a factor of 4:

4I = 4 ⁻¹(2) - ln(5)

Compare with a ⁻¹(2) - b ₑ(5):

a = 4, b = 1

Therefore, 2a + b = 2(4) + 1 = 9.

Pattern Recognition

Always convert ⁻¹ quadratic inputs into ⁻¹(x-y)/(1+xy) forms. Apply King's property on symmetric limits; often one piece vanishes entirely.

Chapter Mix

Class 12 Maths: Definite Integrals Class 12 Maths: Inverse Trigonometric Functions

Q15 jee_main_2026_22_january_morning Properties of Definite Integrals
The value of ∫-(π)/(2)(π)/(2)((1)/([x]+4))dx, where [ ] denotes the greatest integer function, is
  • A. (1)/(60)(21π-1)
  • B. (1)/(60)(π-7)
  • C. (7)/(60)(3π-1)
  • D. (7)/(60)(π-3)

Solution

Related Formula
The greatest integer function [x] is piecewise constant on intervals [n, n+1). ∫ₐb f(x) dx is broken into sub-intervals where f(x) is constant.
Core Logic

The integral bounds are from -π/2 ≈ -1.57 to π/2 ≈ 1.57. We must split the integral at every integer point between these bounds.

Intervals:

  • [-π/2, -1) [x] = -2
  • [-1, 0) [x] = -1
  • [0, 1) [x] = 0
  • [1, π/2) [x] = 1
Step 1: Splitting the Integral
I = ∫-π/2π/2(1)/([x]+4)dx I = ∫-π/2⁻¹ (1)/(-2 + 4) dx + ∫₋₁⁰ (1)/(-1 + 4) dx + ∫₀¹ (1)/(0 + 4) dx + ∫₁π/2 (1)/(1 + 4) dx
Step 2: Evaluating Sub-integrals
I = ∫-π/2⁻¹ (1)/(2) dx + ∫₋₁⁰ (1)/(3) dx + ∫₀¹ (1)/(4) dx + ∫₁π/2 (1)/(5) dx

Evaluate the limits for each constant integral:

I = (1)/(2) ( -1 - (-(π)/(2)) ) + (1)/(3) (0 - (-1)) + (1)/(4) (1 - 0) + (1)/(5) ( (π)/(2) - 1 ) I = (1)/(2) ( (π)/(2) - 1 ) + (1)/(3) + (1)/(4) + (1)/(5) ( (π)/(2) - 1 )
Step 3: Simplifying the Expression

Group the ( (π)/(2) - 1 ) terms:

I = ((1)/(2) + (1)/(5)) ( (π)/(2) - 1 ) + (1)/(3) + (1)/(4) I = (7)/(10) ( (π)/(2) - 1 ) + (7)/(12) I = (7π)/(20) - (7)/(10) + (7)/(12)

Find a common denominator for the constants (LCD is 60):

-(7)/(10) + (7)/(12) = -(42)/(60) + (35)/(60) = -(7)/(60)

Rewrite (7π)/(20) with denominator 60:

(7π)/(20) = (21π)/(60)

So,

I = (21π)/(60) - (7)/(60) = (7(3π - 1))/(60) = (7)/(60)(3π - 1)
Pattern Recognition

Integration of step functions always transforms into a simple sum of rectangle areas (cᵢ × Δ xᵢ). Immediately break the bounds at integers, turning a calculus problem into elementary arithmetic.

Chapter Mix

Class 12 Maths: Definite Integration

Q23 jee_main_2026_22_january_morning Integration by Substitution
If ∫( x)(-11)/(2)( x)(-5)/(2)dx= - p₁q₁( x)(9)/(2)- p₂q₂( x)(5)/(2)- p₃q₃( x)(1)/(2)+ p₄q₄( x)(-3)/(2)+C, where pᵢ and qᵢ are positive integers with (pᵢ, qᵢ)=1 for i=1, 2, 3, 4 and C is the constant of integration, then 15p₁p₂p₃p₄q₁q₂q₃q₄ is equal to ____.
Numerical Answer. Answer: 16 to 16

Solution

Related Formula
When powers of sine and cosine add up to a negative even integer, extract ² x and substitute x = t
Core Logic

Integral: I = ∫ -11/2 x -5/2 x dx

The sum of powers is -(11)/(2) - (5)/(2) = -8. Convert the integrand entirely into terms of x and x by dividing and multiplying by -11/2 x.

I = ∫ (( x)/( x))-11/2 -11/2 x -5/2 x dx I = ∫ ( x)-11/2 ( x)⁻⁸ dx I = ∫ ( x)-11/2 ⁸ x dx
Step 1: Integration by Substitution

Rewrite ⁸ x = ( ² x)³ ² x = (1 + ² x)³ ² x.

I = ∫ ( x)-11/2 (1 + ² x)³ ² x dx

Substitute t = x dt = ² x dx.

I = ∫ t-11/2 (1 + t²)³ dt

Expand (1 + t²)³ = 1 + 3t² + 3t⁴ + t⁶.

I = ∫ t-11/2 (1 + 3t² + 3t⁴ + t⁶) dt I = ∫ (t-11/2 + 3t-7/2 + 3t-3/2 + t1/2) dt
Step 2: Evaluating the Anti-derivatives

Integrate term by term:

I = t-9/2-9/2 + 3 t-5/2-5/2 + 3 t-1/2-1/2 + t3/23/2 + C I = -(2)/(9)t-9/2 - (6)/(5)t-5/2 - 6t-1/2 + (2)/(3)t3/2 + C

Substitute back t = x = (1)/( x), which implies t-a = ( x)^a.

I = -(2)/(9)( x)9/2 - (6)/(5)( x)5/2 - (6)/(1)( x)1/2 + (2)/(3)( x)-3/2 + C
Step 3: Variable Assignment

Comparing with -(p₁)/(q₁)( x)9/2 - (p₂)/(q₂)( x)5/2 - (p₃)/(q₃)( x)1/2 + (p₄)/(q₄)( x)-3/2:

p₁ = 2, q₁ = 9 p₂ = 6, q₂ = 5 p₃ = 6, q₃ = 1 p₄ = 2, q₄ = 3

Calculate (15 p₁ p₂ p₃ p₄)/(q₁ q₂ q₃ q₄):

= (15(2)(6)(6)(2))/((9)(5)(1)(3)) = (15 × 144)/(135) = (2160)/(135) = 16
Pattern Recognition

If ∫ ^m x ⁿ x dx has m+n as a negative even integer, unconditionally extract |m+n|x and set x = t. The expansion expands gracefully into polynomial power rules without any trig substitution hassle.

Chapter Mix

Class 12 Maths: Indefinite Integration

More Definite Integrals Questions — jee_main_2025_24_jan_morning

Practice all Definite Integrals previous-year questions →

Rankbit System
JEE Physics: Waves (+15.5%) | Electrostatics: Concentric Shells (-29.7%) | Modern Physics: Photoelectric Clones (+34.2%) | Mathematics: Definite Integrals (+18.1%) | Chemistry: Coordination Splitting (-11.4%) | JEE Physics: Waves (+15.5%) | Electrostatics: Concentric Shells (-29.7%) | Modern Physics: Photoelectric Clones (+34.2%) | Mathematics: Definite Integrals (+18.1%) | Chemistry: Coordination Splitting (-11.4%)