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GATE | GATE CS 2018 | Question 25

Last Updated : 23 Feb, 2018
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The value of \int_{0}^{\pi / 4} x \cos(x^2) dx correct to three decimal places (assuming that \pi = 3.14) is _______ . Note –This was Numerical Type question. (A) 0.289 (B) 0.389 (C) 0.829 (D) 0.428

Answer: (A)

Explanation:
\int_{0}^{\pi / 4} x \cos(x^2) dx = \int_{0}^{\pi / 4} x \cos(t) \frac{dt}{2x} Let X2 = t 2x.dx = dt dx = \frac {dt}{2x}   Limits : x = 0,  \frac{\pi} {4} t = 0, ( \frac{\pi} {4} )^2   \int_{0}^{(\pi / 4)^2} \frac{\Cos(t)}{2} dt = \left [\frac{\Sin t}{2} \right ]_{0}^{(\pi / 4)^2} Since (π/4)2 = 0.616  \left [\frac{\sin{(\pi / 4)}^2}{2}  - \frac{\sin 0}{2}\right ] = \frac{0.5777}{2} - 0 = 0.289

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