MCQ
$\int_{\pi / 4}^{3 \pi / 4} \frac{d x}{1+\cos x}$ is equal to
  • 2
  • B
    -2
  • C
    $\frac{1}{2}$
  • D
    $-\frac{1}{2}$

Answer

Correct option: A.
2
(A)
$\int_{\pi / 4}^{3 \pi / 4} \frac{d x}{1+\cos x}$
$=\int_{\pi / 4}^{3 \pi / 4} \frac{1-\cos x}{1-\cos ^2 x} d x=\int_{\pi / 4}^{3 \pi / 4} \frac{1-\cos x}{\sin ^2 x} d x$
$=\int_{\pi / 4}^{3 \pi / 4}\left(\operatorname{cosec}^2 x-\cot x \operatorname{cosec} x\right) d x$
$=[-\cot x+\operatorname{cosec} x]_{\frac{\pi}{4}}^{\frac{3 \pi}{4}}=2$

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