Question 18

Mathematics Definite Integrals Medium

The value of \( \int_{0}^{\sin ^{2} x} \sin ^{-1} \sqrt {t} d t+\int_{0}^{\cos ^{2} x} \cos ^{-1} \sqrt {t} d t \) is

(A) \( \frac{\pi}{4} \)
(B) \( \frac{\pi}{2} \)
(C) 1
(D) None
✓ Correct Answer: Option D Verified Solution

📘 Step-by-Step Solution & Detailed Explanation:

We need to evaluate: \[ I = \int_{0}^{\sin^2 x} \sin^{-1} (5t) \, dt + \int_{0}^{\cos^2 x} \cos^{-1} (5t) \, dt \] We use the property: \[ \sin^{-1} y + \cos^{-1} y = \frac{\pi}{2} \] So, \[ \sin^{-1} (5t) + \cos^{-1} (5t) = \frac{\pi}{2} \] Split the Integral \[ I = \int_{0}^{\sin^2 x} \sin^{-1} (5t) \, dt + \int_{0}^{\cos^2 x} \left( \frac{\pi}{2} - \sin^{-1} (5t) \right) dt \] \[ I = \int_{0}^{\sin^2 x} \sin^{-1} (5t) \, dt + \frac{\pi}{2} \int_{0}^{\cos^2 x} dt - \int_{0}^{\cos^2 x} \sin^{-1} (5t) \, dt \] Since the first and third integrals cancel out, we are left with: \[ I = \frac{\pi}{2} \int_{0}^{\cos^2 x} dt \] \[ = \frac{\pi}{2} \times \cos^2 x \] Since the integral does not yield a fixed value for all \(x\), the answer is None.

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