If $y=\log \sqrt{\tan x}$, then the value of $\frac{d y}{d x}$ at $x=\frac{\pi}{4}$ is

If $y=\log \sqrt{\tan x}$, then the value of $\frac{d y}{d x}$ at $x=\frac{\pi}{4}$ is
  1. 1
  2. $-1$
  3. $\frac{1}{2}$
  4. 0

Solution

$\begin{aligned} & y=\log \sqrt{\tan x} \\ & \therefore \quad \frac{d y}{d x}=\frac{1}{\sqrt{\tan x}} \times \frac{1}{2 \sqrt{\tan x}} \times \sec ^2 x=\frac{\sec ^2 x}{2 \tan x} \\ & \therefore \quad\left(\frac{d y}{d x}\right)_{x=\frac{\pi}{4}}=\frac{(\sqrt{2})^2}{2}=1\end{aligned}$

Asked in: MHT CET 2021 (23 Sep Shift 2)

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