If ∫₀¹ 1√(3+x)+√(1+x)dx=a+b√(2)+c√(3), where a, b, c are rational numbers, then 2a+3b-4c is equal to:

Solution & Explanation

Related Formula
∫ xⁿ dx = xⁿ⁺¹n+1
Core Logic

To evaluate integrals with sum of square roots in the denominator, multiply and divide by the conjugate to rationalize it.

I = ∫₀¹ √(3+x)-√(1+x)(√(3+x)+√(1+x))(√(3+x)-√(1+x))dx I = ∫₀¹ √(3+x)-√(1+x)(3+x) - (1+x)dx I = (1)/(2) ∫₀¹ (√(3+x) - √(1+x)) dx
Step 1: Integration and Bounds Setup

Integrate the resulting expression:

I = (1)/(2) [ (3+x)3/23/2 - (1+x)3/23/2 ]₀¹ I = (1)/(2) · (2)/(3) [ (3+x)3/2 - (1+x)3/2 ]₀¹ I = (1)/(3) [ ((4)3/2 - (2)3/2) - ((3)3/2 - (1)3/2) ]
Step 2: Term Simplification

Evaluate the boundary powers: 43/2 = 8 23/2 = 2√(2) 33/2 = 3√(3) 13/2 = 1

Substitute back into the expression:

I = (1)/(3) [ 8 - 2√(2) - 3√(3) + 1 ] = (1)/(3) [ 9 - 2√(2) - 3√(3) ] I = 3 - (2)/(3)√(2) - √(3)
Step 3: Finding Co-efficients

Comparing with a+b√(2)+c√(3) yields: a = 3, b = -(2)/(3), c = -1

Compute 2a+3b-4c:

2(3) + 3(-(2)/(3)) - 4(-1)

6 - 2 + 4 = 8

Pattern Recognition

Whenever you see a sum of square roots in the denominator of an integrand, the immediate algorithmic next step is rationalization.

Chapter Mix

Class 12 Maths: Definite Integration

Reference Study Guides

More Definite Integration 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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