$\int[\sin |\log x|+\cos |\log x|] d x=$
$\int[\sin |\log x|+\cos |\log x|] d x=$
- $\sin |\log x|+c$
- $\cos |\log x|+c$
- $x \cos |\log x|+c$
- $x \sin |\log x|+c$
Solution
Let $\mathrm{I}=\int[\sin |\log \mathrm{x}|+\cos |\log \mathrm{x}|] \mathrm{dx}$
Put $\log \mathrm{x}=\mathrm{t} \Rightarrow \frac{1}{\mathrm{x}} \mathrm{dx}=\mathrm{dt} \Rightarrow \mathrm{dx}=\mathrm{e}^{\mathrm{t}} \mathrm{dt}$
$\begin{aligned}
& \therefore \mathrm{I}=\int(\sin +\cos t) \mathrm{e}^{\mathrm{t}} d t \\
& =\int \mathrm{e}^{\mathrm{t}}(\sin \mathrm{t}+\cos t) d t=\mathrm{e}^{\mathrm{t}} \sin \mathrm{t}+\mathrm{c}=\mathrm{x} \sin |\log \mathrm{x}|+\mathrm{c}
\end{aligned}$
Asked in: MHT CET 2021 (21 Sep Shift 2)
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