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
- $\frac{8}{5}$
- 2
- 1
- $\frac{8 e^3}{5}$
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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