The Mountain of Calculus
A Journey Through the Integral
Imagine standing before a massive, jagged mountain. That is exactly what this integral looks like at first glance:
I=∫(x1+x31)(3x−24+x−26)231dx
It is intimidating, filled with negative powers and a fractional exponent that seems designed to confuse. But in the world of JEE Advanced, every complex problem is just a series of simple, elegant steps waiting to be uncovered. Let us climb this mountain together.
Phase 1
The Art of Factoring
The secret to conquering this integral lies in the term (3x−24+x−26)231. We need to simplify this. The intuition here is to factor out a power of x from inside the bracket that will perfectly cancel with the 231 exponent.
If we factor out x−23, we get:
(3x−24+x−26)231=[x−23(3x−1+x−3)]231
Now, applying the property (ab)n=anbn, we get (x−23)231(3x−1+x−3)231, which simplifies beautifully to x−1(3x−1+x−3)231. This is the breakthrough!
Phase 2
The Bridge to Simplicity
Now, let us bring this back to our integral. The expression becomes:
I=∫(x1+x31)x−1(3x−1+x−3)231dx
If we distribute the x−1 into the first bracket (x1+x31), we get (x−2+x−4). Our integral is now:
I=∫(x−2+x−4)(3x−1+x−3)231dx
Do you see the beauty of this? The term outside the bracket is almost exactly the derivative of the term inside the bracket. This is the classic setup for the method of substitution.
Phase 3
The Substitution
Let us set u=3x−1+x−3. Now, we differentiate with respect to x:
dxdu=3(−1)x−2+(−3)x−4=−3(x−2+x−4)
This means (x−2+x−4)dx=−31du. Substituting this into our integral, we get:
I=∫u231(−31)du=−31∫u231du
The mountain has suddenly become a gentle hill. We can now use the standard power rule for integration: ∫undu=n+1un+1+C. Adding one to the power 231 gives us 2324.
So, the integral is:
I=−31[2324u2324]+C=−31⋅2423u2324+C=−3(24)23u2324+C
Phase 4
The Final Victory
We are almost at the summit. Substituting u=3x−1+x−3 back into our result, we get:
I=−3(24)23(3x−1+x−3)2324+C
Now, we compare this to the target form: −3(α+1)α(3xβ+xγ)αα+1+C. By direct comparison, we identify α=23, β=−1, and γ=−3.
The final step is just simple arithmetic:
We have reached the top! The complex integral has been solved, and the answer is 19. Remember, no matter how terrifying a problem looks, there is always a path to the solution if you break it down step by step.