$\int e^{\cos ^{-1} x}\left[\frac{x-\sqrt{1-x^{2}}}{\sqrt{1-x^{2}}}\right] d x=$
$\int e^{\cos ^{-1} x}\left[\frac{x-\sqrt{1-x^{2}}}{\sqrt{1-x^{2}}}\right] d x=$
- $-e^{\sin ^{-1} x}+c$
- $-x e^{\cos ^{-1} x}+c$
- $-x e^{\sin ^{-1} x}+c$
- $-e^{\cos ^{-1} x}+c$
Solution
Put $\cos ^{-1} x=t \Rightarrow \frac{-1}{\sqrt{1-x^{2}}} d x=d t \Rightarrow \frac{1}{\sqrt{1-x^{2}}} d x=-d t$ and $x=\cos t$
$\begin{aligned} I &=-\int e^{t}[\cos t-\sin t] d t=-e^{t} \cos t+c \\ &=-e^{\cos ^{-1} x} \cos \left(\cos ^{-1} x\right)+c=-x e^{\cos ^{-1} x}+c \end{aligned}$
Asked in: MHT CET 2020 (12 Oct Shift 1)
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