Sigma Percentile
JEE Main 2021 (27 Aug Shift 1)
LEVELBoard

Animated Solution for Mathematics - Definite Integration: is equal to:

Select Answer:

Visualized Solution

The Given Integral

  • Let the given integral be :

Analyzing the Denominator

  • Focus on the quadratic expression:
  • Observe that and
  • So,

Factorizing the Expression

  • Using the identity :
  • The integral becomes:

The King's Property

  • Apply the property:
  • Here, and
  • Sum of limits:

Substituting the Variable

  • Replace with in the integral:

Simplifying the New Integral

  • Simplify the second term in the denominator:
  • New form of :

Adding the Two Integrals

  • Add the original and the new expressions for :

Evaluating the Simple Integral

  • The integrand simplifies to :

Final Calculation

  • The correct option is 5.

The Sigma Insight: Fundamental Theorem & Properties of Definite Integrals

Analyzing the Setup

Welcome, fellow traveler on the path to JEE excellence. Today, we are not just solving an integral; we are uncovering a hidden symmetry.
When you first look at the expression
it might seem intimidating. It looks like a complex mess of logarithms and quadratics, but in the world of competitive mathematics, complexity is often just a mask for elegance.

The Hidden Identity

Let us look at the denominator. Specifically, focus your attention on the quadratic expression .
If you have been practicing your algebraic identities, you might notice that is the square of , and is exactly . This is the classic expansion of .
By recognizing this, we transform our integral into:

The King's Property

The King's Property states that for any continuous function on the interval , the integral is equal to .
Here, our limits are and . Their sum is . This is not a coincidence; it is a mathematical invitation.
By replacing with , we are essentially looking at the function from the other side of the mirror. Let us perform the substitution:
Look closely at the second term in the denominator. The expression simplifies beautifully to , which is just .
Our new integral is:

The Grand Cancellation

Now, we have two versions of . If we add them together, something magical happens.
The denominators are identical, and the numerators add up to the exact same expression as the denominator:
Because the numerator and denominator are now the same, the entire integrand collapses into . We are left with the simplest integral imaginable:
Evaluating this is straightforward:
Therefore, the final result is:

Final Reflections

We started with a complex logarithmic expression, and through the power of symmetry and the King's Property, we reduced it to a simple subtraction. This is the beauty of JEE mathematics.
It is not about brute force; it is about finding the right perspective. Whenever you face a difficult integral, pause, look for the symmetry, and look for the perfect squares. The answer is often hiding in plain sight, waiting for you to apply the right property.

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