If ∫( 1-5 ²x ⁵x ²x)dx=f(x)+C where C is the constant of integration, then f((π)/(6))-f((π)/(4)) is equal to

Solution & Explanation

Core Logic

Split the integral into two terms:

I = ∫ (1)/( ⁵ x ² x) dx - ∫ (5 ² x)/( ⁵ x ² x) dx I = ∫ ( ² x)/( ⁵ x) dx - 5 ∫ (1)/( ⁵ x) dx
Step 1: Integration by Parts

Take the first integral I₁ = ∫ (1)/( ⁵ x) · ² x dx. Apply Integration by Parts taking u = (1)/( ⁵ x) and dv = ² x dx:

I₁ = (1)/( ⁵ x) · x - ∫ ( -(5 x)/( ⁶ x) ) x dx I₁ = ( x)/( ⁵ x) + 5 ∫ ( x)/( ⁶ x) · ( x)/( x) dx I₁ = ( x)/( ⁵ x) + 5 ∫ (1)/( ⁵ x) dx
Step 2: Re-substituting into Total Integral
I = ( ( x)/( ⁵ x) + 5 ∫ (1)/( ⁵ x) dx ) - 5 ∫ (1)/( ⁵ x) dx

The integral terms exactly cancel out:

I = ( x)/( ⁵ x) + C

Thus, f(x) = ( x)/( ⁵ x).

Step 3: Function Evaluation

Calculate f((π)/(6)):

f((π)/(6)) = ( (π/6))/( ⁵(π/6)) = 1/√(3)(1/2)⁵ = 32√(3)

Calculate f((π)/(4)):

f((π)/(4)) = ( (π/4))/( ⁵(π/4)) = 1(1/√(2))⁵ = (√(2))⁵ = 4√(2)

Difference:

f((π)/(6)) - f((π)/(4)) = 32√(3) - 4√(2) = 4√(3)(8 - √(6))
Pattern Recognition

Integrals of the form ∫ (complicated term 1 - complicated term 2) dx often cancel perfectly when Integration by Parts is applied to just one of the terms. Look for derivative relationships between the numerators.

Chapter Mix

Class 12 Mathematics: Integrals

Reference Study Guides

More Integrals Previous-Year Questions — Page 5

Q71 jee_main_2025_02_april_morning Definite Integration with GIF
Let [·] denote the greatest integer function. If ∫₀^e³[ 1ex - 1]dx = α - ₑ2, then α³ is equal to ________.
Numerical Answer. Answer: 8 to 8

Solution

Related Formula

Greatest Integer Function boundaries:

[f(x)] = k for k ≤ f(x) < k+1, k in Z
Core Logic

Analyze the value variations of f(x) = e1-x across the integration limits [0, e³] to break down the integral into distinct piecewise continuous intervals.

Step 1: Determine Step Function Transition Points

Let y = e1-x.

  • At x = 0 y = e¹ ≈ 2.718
  • As x increases, e1-x decreases monotonically.
  • Find x where y = 2 e1-x = 2 1-x = ln 2 x = 1 - ln 2.
  • Find x where y = 1 e1-x = 1 1-x = 0 x = 1.
  • At the final boundary x = e³ y = e1-e³, which is a very small positive decimal strictly inside (0,1).
Step 2: Split the Definite Integral

Rewrite the integral based on the isolated interval blocks:

I = ∫₀1-ln 2 2 dx + ∫1-ln 2¹ 1 dx + ∫₁e³ 0 dx
Step 3: Perform Integrations
I = 2[x]₀1-ln 2 + 1[x]1-ln 2¹ + 0 I = 2(1 - ln 2 - 0) + 1(1 - (1 - ln 2)) = 2 - 2ln 2 + ln 2 = 2 - ln 2
Step 4: Solve for Alpha Cubed

Compare the integrated value to α - ln 2:

α - ln 2 = 2 - ln 2 α = 2 α³ = 2³ = 8
Pattern Recognition

Always map the function values at the extreme boundary points first. Tracking the downward path from 2.71 arrow 2 arrow 1 arrow 0 reveals exactly where the integer thresholds are crossed.

Chapter Mix

Class 12 Mathematics: Integrals

Q59 jee_main_2025_03_april_evening Definite Integrals
The integral ∫₀^π (8x dx)/(4 ² x + ² x) is equal to
  • A. 2π²
  • B. 4π²
  • C. π²
  • D. (3π²)/(2)

Solution

Related Formula

Using the properties of definite integrals:

∫ₐ^b f(x) dx = ∫ₐ^b f(a+b-x) dx

Also, if f(2a-x) = f(x), then:

∫₀2a f(x) dx = 2 ∫₀^a f(x) dx
Core Logic

Let:

I = ∫₀^π (8x dx)/(4 ² x + ² x) --- (1)

Applying x → π-x:

I = ∫₀^π (8(π - x) dx)/(4 ² x + ² x) --- (2)
Step 1: Eliminating the x term in numerator

Adding (1) and (2):

2I = 8π ∫₀^π (dx)/(4 ² x + ² x) I = 4π ∫₀^π (dx)/(4 ² x + ² x)

Since the integrand is symmetric about x = π/2:

I = 8π ∫₀π/2 (dx)/(4 ² x + ² x)
Step 2: Integration using ² x substitution

Divide numerator and denominator by ² x:

I = 8π ∫₀π/2 ( ² x dx)/(4 + ² x)

Let t = x dt = ² x dx At x = 0, t = 0; at x = π/2, t → ∞.

I = 8π ∫₀^∞ (dt)/(t² + 2²) I = 8π [ (1)/(2) ⁻¹((t)/(2)) ]₀^∞ = 4π ( (pi)/(2) - 0 ) = 2π²
Pattern Recognition

The presence of a linear x factor in the numerator of a definite integral with symmetric trigonometric bounds is almost always eliminated using the a+b-x property. This reduces the integral to a standard substitution problem.

Chapter Mix

Class 12 Mathematics: Integrals

Q60 jee_main_2025_07_april_morning Properties of Definite Integrals
The integral ∫₀^π ((x + 3) x)/(1 + 3 ²x) dx is equal to:
  • A. π√(3) (π + 1)
  • B. π√(3) (π + 2)
  • C. π3√(3) (π + 6)
  • D. π2√(3) (π + 4)

Solution

Related Formula

King's Property of Definite Integrals:

∫ₐ^b f(x) dx = ∫ₐ^b f(a + b - x) dx
Core Logic

Let the given integral be:

I = ∫₀^π ((x + 3) x)/(1 + 3 ²x) dx (1)

Applying King's property (x → π - x):

I = ∫₀^π ((π - x + 3) (π - x))/(1 + 3 ²(π - x)) dx I = ∫₀^π ((π - x + 3) x)/(1 + 3 ²x) dx (2)
Step 1: Eliminate the x Variable

Adding equations (1) and (2):

2I = ∫₀^π ([(x + 3) + (π - x + 3)] x)/(1 + 3 ²x) dx 2I = (π + 6)∫₀^π ( x)/(1 + 3 ²x) dx

Using the symmetric property ∫₀2a f(x)dx = 2∫₀^a f(x)dx if f(2a-x)=f(x):

2I = 2(π + 6)∫₀π/2 ( x)/(1 + 3 ²x) dx I = (π + 6)∫₀π/2 ( x)/(1 + 3 ²x) dx
Step 2: Solve Using Substitution

Let t = √(3) x. Then dt = -√(3) x dx x dx = - dt√(3). Change in integration boundaries:

  • When x = 0 t = √(3)
  • When x = π/2 t = 0
  • Substituting into the integral:

I = (π + 6) ∫√(3)⁰ -dt/√(3)1 + t² = π + 6√(3) ∫₀√(3) (dt)/(1 + t²) I = π + 6√(3) [ ⁻¹t ]₀√(3) = π + 6√(3) ( ⁻¹√(3) - 0 ) I = π + 6√(3) · (π)/(3) = π3√(3)(π + 6)
Pattern Recognition

Whenever you encounter a linear x factor multiplying trigonometric components in a definite integral with symmetric limits like 0 to π, executing King's property first is almost guaranteed to cleanly wipe out that variable element.

Chapter Mix

Class 12 Mathematics: Definite Integrals

Q58 jee_main_2025_08_april_evening Properties of Definite Integrals
Let f(x) be a a positive function and I₁ = ∫-(1)/(2)¹ 2xf(2x(1 - 2x)) dx and I₂ = ∫₋₁² f(x(1 - x)) dx. Then the value of (I₂)/(I₁) is equal to
  • A. 9
  • B. 6
  • C. 12
  • D. 4

Solution

Related Formula
∫ₐb f(x) dx = ∫ₐb f(a+b-x) dx
Core Logic

Perform variable substitution to match the arguments and limit bounds across both separate integral functions before invoking King's property.

Step 1: Perform Base Transformation Substitution

In I₁, let 2x = t 2dx = dt. Limits mapping: x = -1/2 t = -1; x = 1 t = 2.

I₁ = (1)/(2) ∫₋₁² t f(t(1-t)) dt 2I₁ = ∫₋₁² t f(t(1-t)) dt
Step 2: Invoke Integral Mirror Properties

Apply the identity using parameters (a+b-t) = (1-t):

2I₁ = ∫₋₁² (1-t) f((1-t)(1-(1-t))) dt 2I₁ = ∫₋₁² f(t(1-t)) dt - ∫₋₁² t f(t(1-t)) dt
Step 3: Final Matrix Matching Evaluation

Notice component blocks align exactly with I₂ definition values:

2I₁ = I₂ - 2I₁ 4I₁ = I₂ (I₂)/(I₁) = 4
Pattern Recognition

Symmetric transformations highlighting factor expressions like x(1-x) coupled with an external linear multiplier term x naturally simplify to half-weight area forms using reflection rules.

Chapter Mix

Class 12 Mathematics: Definite Integrals

Q61 jee_main_2025_08_april_evening Integration of Absolute Value Functions
The integral ∫₋₁(3)/(2)(|π²x (π x)|) dx is equal to :
  • A. 3 + 2π
  • B. 4 + π
  • C. 1 + 3π
  • D. 2 + 3π

Solution

Related Formula
∫ x (π x) dx = -(x)/(π) (π x) + ( (π x))/(π²)
Core Logic

Track sign configurations across the target integration segments to drop absolute modulus walls effectively at clean quadrant intervals.

Step 1: Break Apart the Modulus Domain

For x in [-1, 1], product value elements x (π x) ≥ 0. For x in [1, 3/2], values drop below zero:

I = π² ∫₋₁¹ x (π x) dx - ∫₁3/2 x (π x) dx
Step 2: Integrate the Even Function Block

Since x (π x) is symmetric and even:

∫₋₁¹ x (π x) dx = 2 ∫₀¹ x (π x) dx = 2 [ -(x)/(π) (π x) + ( (π x))/(π²) ]₀¹ = (2)/(π)
Step 3: Subtract the Inverse Segment

Evaluating boundary limits across the secondary phase track:

∫₁3/2 x (π x) dx = [ -(x)/(π) (π x) + ( (π x))/(π²) ]₁3/2 = ( 0 - (1)/(π²) ) - ( (1)/(π) ) = -(1)/(π²) - (1)/(π) I = π² (2)/(π) - (-(1)/(π²) - (1)/(π)) = π² ( (3)/(π) + (1)/(π²) ) = 3π + 1
Pattern Recognition

Products of two odd tracking metrics (like linear variable x matched with sinusoidal waves) yield overall even systems, enabling rapid evaluation over center-aligned domains.

Chapter Mix

Class 12 Mathematics: Definite Integrals

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