For $x^2-4 \neq 0$, the value of $\frac{d}{d x}\left[\log…

For $x^2-4 \neq 0$, the value of $\frac{d}{d x}\left[\log \left\{e^x\left(\frac{x-2}{x+2}\right)^{\frac{3}{4}}\right\}\right]$ at $x=3$ is
  1. $\frac{8}{5}$
  2. 2
  3. 1
  4. $\frac{8 e^3}{5}$

Solution

Let $y=\log \left\{e^x\left(\frac{x-2}{x+2}\right)^{\frac{3}{4}}\right\}$ $ \begin{aligned} & =\log e^x+\log \left(\frac{x-2}{x+2}\right)^{\frac{3}{4}}=x \log e+\frac{3}{4} \log \left(\frac{x-2}{x+2}\right) \\ & =x+\frac{3}{4} \log \left(\frac{x-2}{x+2}\right) \end{aligned} $ Now, differentiating w.r.t. $x$, we get $ \begin{aligned} & \frac{d y}{d x}=1+\frac{3}{4} \frac{d}{d x} \log \left(\frac{x-2}{x+2}\right) \\ & =1+\frac{3}{4}\left[\frac{x+2}{x-2} \cdot\left\{\frac{(x+2) \cdot 1-(x-2) \cdot 1}{(x+2)^2}\right\}\right] \\ & =1+\frac{3}{4} \times \frac{4}{x^2-4}=1+\frac{3}{x^2-4} \\ & \text { At } x=3, \\ & \left(\frac{d y}{d x}\right)_{x=3}=1+\frac{3}{5}=\frac{8}{5} \end{aligned} $

Asked in: AP EAMCET 2017 (26 Apr Shift 1)

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