If $\mathrm{f}^{\prime}(x)=\sin (\log x)$ and $y=\mathrm{f}\left(\frac{2 x+3}{3-2 x}\right)$, then…
If $\mathrm{f}^{\prime}(x)=\sin (\log x)$ and $y=\mathrm{f}\left(\frac{2 x+3}{3-2 x}\right)$, then $\frac{\mathrm{d} y}{\mathrm{~d} x}$ at $x=1$ is
- $6 \sin (\log 5)$
- $5 \sin (\log 6)$
- $12 \sin (\log 5)$
- $5 \sin (\log 12)$
Solution
$\begin{aligned} & y=\mathrm{f}\left(\frac{2 x+3}{3-2 x}\right) \\ & \therefore \quad \frac{\mathrm{d} y}{\mathrm{~d} x}=\mathrm{f}^{\prime}\left(\frac{2 x+3}{3-2 x}\right) \cdot \frac{\mathrm{d}}{\mathrm{d} x}\left(\frac{2 x+3}{3-2 x}\right) \\ & =\mathrm{f}^{\prime}\left(\frac{2 x+3}{3-2 x}\right) \cdot \frac{(3-2 x) \cdot 2-(2 x+3)(-2)}{(3-2 x)^2} \\ & =\sin \left[\log \left(\frac{2 x+3}{3-2 x}\right)\right] \cdot \frac{12}{(3-2 x)^2} \\ & \therefore \quad\left(\frac{\mathrm{d} y}{\mathrm{~d} x}\right)_{x=1}=\sin (\log 5) \cdot 12=12 \sin (\log 5) \\ & \end{aligned}$
Asked in: MHT CET 2023 (14 May Shift 2)
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