If $\mathrm{f}(x)=\log _{x^2}\left(\log _{\mathrm{e}} x\right)$, then $\mathrm{f}^{\prime}(x)$ at…

If $\mathrm{f}(x)=\log _{x^2}\left(\log _{\mathrm{e}} x\right)$, then $\mathrm{f}^{\prime}(x)$ at $x=\mathrm{e}$ is
  1. 1
  2. $\frac{1}{\mathrm{e}}$
  3. $\frac{1}{2 \mathrm{e}}$
  4. $\frac{1}{4 \mathrm{e}}$

Solution

$\begin{aligned} f(x) & =\log _{x^2}\left(\log _{\mathrm{e}} x\right) \\ & =\frac{\log \left(\log _{\mathrm{e}} x\right)}{\log x^2} \\ & =\frac{\log \left(\log _{\mathrm{e}} x\right)}{2 \log x}\end{aligned}$ $\therefore \quad \mathrm{f}^{\prime}(x)=\frac{1}{2}\left[\frac{\log x \cdot \frac{1}{\log _{\mathrm{e}} x} \cdot \frac{\mathrm{~d}}{\mathrm{~d} x}(\log x)-\log \left(\log _{\mathrm{e}} x\right) \cdot \frac{1}{x}}{(\log x)^2}\right]$ $\therefore \quad \mathrm{f}^{\prime}(x)=\frac{1}{2}\left[\frac{\frac{1}{x}-\frac{\log \left(\log _{\mathrm{e}} x\right)}{x}}{(\log x)^2}\right]$ $\therefore \quad \mathrm{f}^{\prime}(\mathrm{e})=\frac{1}{2}\left[\frac{\frac{1}{\mathrm{e}}-0}{(1)^2}\right]=\frac{1}{2 \mathrm{e}}$

Asked in: MHT CET 2024 (02 May Shift 2)

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