$\int_0^{\frac{\pi}{2}} \frac{\sin x-\cos x}{1-\sin x \cos x} d x=$

$\int_0^{\frac{\pi}{2}} \frac{\sin x-\cos x}{1-\sin x \cos x} d x=$
  1. $\frac{\pi}{4}$
  2. $\frac{2}{\pi}$
  3. 0
  4. $\frac{\pi}{2}$

Solution

Let $I=\int_0^{\pi / 2} \frac{\sin x-\cos x}{1-\sin x \cos x} d x$ $\begin{aligned} & \therefore I=\int_0^{\frac{\pi}{2}} \frac{\sin \left(\frac{\pi}{2}-x\right)-\cos \left(\frac{\pi}{2}-x\right)}{1-\sin \left(\frac{\pi}{2}-x\right) \cos \left(\frac{\pi}{2}-x\right)} d x \\ & =\int_0^{\pi / 2} \frac{\cos x-\sin x}{1-\cos x \sin x} d x \end{aligned}$ Eq. (1) $+(2)$ gives $2 \mathrm{I}=\int_0^{\frac{\pi}{2}} 0 \mathrm{dx} \Rightarrow \mathrm{I}=0$

Asked in: MHT CET 2021 (21 Sep Shift 1)

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