If $\int_0^{\mathrm{k}} \frac{d x}{2+8 x^2}=\frac{\pi}{16}$, then value of $\mathrm{k}$ is

If $\int_0^{\mathrm{k}} \frac{d x}{2+8 x^2}=\frac{\pi}{16}$, then value of $\mathrm{k}$ is
  1. $4$
  2. $\frac{1}{2}$
  3. $\frac{1}{4}$
  4. $2$

Solution

$\begin{aligned} & \int_0^k \frac{d x}{2+8 x^2}=\frac{\pi}{16} \Rightarrow \frac{1}{2} \int_0^k \frac{d x}{1+(2 x)^2}=\frac{\pi}{16} \\ & \Rightarrow \frac{1}{2}\left[\frac{\tan ^{-1}(2 x)}{2}\right]_0^k=\frac{\pi}{16} \\ & \Rightarrow \tan ^{-1}(2 k)=\frac{\pi}{16} \\ & \Rightarrow 2 k=1 \\ & \Rightarrow k=\frac{1}{2}\end{aligned}$

Asked in: MHT CET 2022 (06 Aug Shift 1)

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