Question 31

Mathematics Definite Integrals Hard

Match List - I with List - II

List - I List - II
(A) \( \int_{0}^{\frac{\pi}{2}} \frac{\sin ^{4} \mathrm{x}}{\sin ^{4} \mathrm{x}+\cos ^{4} \mathrm{x}} \mathrm{dx} \) (I) 0
(B) \( \int_{\frac{\pi}{6}}^{\frac{\pi}{3}} \frac{1}{1+\sqrt{\tan x}} d x \) (II) 1
(C) \( \int_{0}^{1} x e^{x} d x \) (III) \( \frac{\pi}{12} \)
(D) \( \int_{-1}^{1} \mathrm{x}^{109} \cos ^{88} \mathrm{xdx} \) (IV) \( \frac{\pi}{4} \)
Choose the correct answer from the options given below:

(A) [(A - IV); (B - III); (C - I); (D - II)]
(B) [(A - IV); (B - III); (C - II); (D - I)]
(C) \( [(\mathrm{A}-\mathrm{III}) ;(\mathrm{B}-\mathrm{IV}) ;(\mathrm{C}-\mathrm{II}) ;(\mathrm{D}-\mathrm{I})] \)
(D) \( [(\mathrm{A}-\mathrm{III}) ;(\mathrm{B}-\mathrm{IV}) ;(\mathrm{C}-\mathrm{I}) ;(\mathrm{D}-\mathrm{II})] \)
View Dynamic Solution & Explanation
Correct Solution: Option B

Step-by-step Solution:

To solve the matching problem, let's evaluate each integral in List - I and match it with the corresponding value in List - II.
(A) \( \int_{0}^{\frac{\pi}{2}} \frac{\sin^{4}x}{\sin^{4}x + \cos^{4}x} \, dx \)
We use the property of definite integrals: \[ \int_{0}^{\frac{\pi}{2}} \frac{\sin^{4}x}{\sin^{4}x + \cos^{4}x} \, dx = \int_{0}^{\frac{\pi}{2}} \frac{\cos^{4}x}{\sin^{4}x + \cos^{4}x} \, dx \] Adding these two integrals: \[ 2I = \int_{0}^{\frac{\pi}{2}} \frac{\sin^{4}x + \cos^{4}x}{\sin^{4}x + \cos^{4}x} \, dx = \int_{0}^{\frac{\pi}{2}} 1 \, dx = \frac{\pi}{2} \] Thus: \[ I = \frac{\pi}{4} \] So, (A) matches with (IV).
(B) \( \int_{\frac{\pi}{6}}^{\frac{\pi}{3}} \frac{1}{1+\sqrt{\tan x}} \, dx \) Let \( I = \int_{\frac{\pi}{6}}^{\frac{\pi}{3}} \frac{1}{1+\sqrt{\tan x}} \, dx \). Using the substitution \( x = \frac{\pi}{2} - t \), we get: \[ I = \int_{\frac{\pi}{6}}^{\frac{\pi}{3}} \frac{1}{1+\sqrt{\cot t}} \, dt \] Adding the two forms of \( I \): \[ 2I = \int_{\frac{\pi}{6}}^{\frac{\pi}{3}} 1 \, dx = \frac{\pi}{3} - \frac{\pi}{6} = \frac{\pi}{6} \] Thus: \[ I = \frac{\pi}{12} \] So, (B) matches with (III).
(C) \( \int_{0}^{1} x e^{x} \, dx \) Using integration by parts: \[ \int x e^{x} \, dx = x e^{x} - \int e^{x} \, dx = x e^{x} - e^{x} + C \] Evaluating from 0 to 1: \[ \int_{0}^{1} x e^{x} \, dx = \left[ x e^{x} - e^{x} \right]_{0}^{1} = (1 \cdot e^{1} - e^{1}) - (0 \cdot e^{0} - e^{0}) = 0 - (-1) = 1 \] So, (C) matches with (II).
(D) \( \int_{-1}^{1} x^{109} \cos^{88}x \, dx \) The integrand \( x^{109} \cos^{88}x \) is an **odd function** because \( x^{109} \) is odd and \( \cos^{88}x \) is even. The integral of an odd function over symmetric limits \([-a, a]\) is zero: \[ \int_{-1}^{1} x^{109} \cos^{88}x \, dx = 0 \] So, (D) matches with (I).

Thus, the correct matching is: \[ \text{A-IV, B-III, C-II, D-I} \]