For $x>1$, if $(2 x)^{2 y}=4 \mathrm{e}^{2 x-2 y}$, then $\left(1+\log _e 2 x\right)^2 \frac{d y}{d x}$ is…

For $x>1$, if $(2 x)^{2 y}=4 \mathrm{e}^{2 x-2 y}$, then $\left(1+\log _e 2 x\right)^2 \frac{d y}{d x}$ is equal to
  1. $\frac{x \log _{\mathrm{e}} 2 x+\log _{\mathrm{e}} 2}{x}$
  2. $\frac{x \log _e 2 x-\log _e 2}{x}$
  3. $x \log _e 2 x+\frac{\log _e 2}{x}$
  4. $x \log _{\mathrm{e}} 2 x-\frac{\log _{\mathrm{e}} 2}{2}$

Solution

$(2 x)^{2 y}=4 \mathrm{e}^{2 x-2 y}$ Taking ' $\log _{\mathrm{e}}$ ' on both sides, we get $2 y \log _{\mathrm{e}}(2 x)=\log _{\mathrm{e}} 4+(2 x-2 y) \log _{\mathrm{e}} \mathrm{e}$ $\therefore \quad y \log _{\mathrm{e}}(2 x)=\log _{\mathrm{e}} 2+x-y$ Differentiating w.r.t. $x$, we get $\begin{array}{ll} & {\left[\log _{\mathrm{e}} 2 x\right] \frac{\mathrm{d} y}{\mathrm{~d} x}+\frac{2 y}{2 x}=0+1-\frac{\mathrm{d} y}{\mathrm{~d} x}} \\ & {\left[1+\log _{\mathrm{e}} 2 x\right] \frac{\mathrm{d} y}{\mathrm{~d} x}=1-\frac{y}{x}} \\ & \text { Now, (i) } \Rightarrow y=\frac{\log _{\mathrm{e}} 2+x}{1+\log _{\mathrm{e}} 2 x} \\ \therefore \quad \ldots \text { (ii) } & \left(\text { ii) } \Rightarrow\left(1+\log _{\mathrm{e}} 2 x\right) \frac{\mathrm{d} y}{\mathrm{~d} x}=\frac{x \log _{\mathrm{e}} 2 x-\log _{\mathrm{e}} 2}{x\left(1+\log _e 2 x\right)}\right. \\ \therefore \quad & \left(1+\log _{\mathrm{e}} 2 x\right)^2 \frac{\mathrm{d} y}{\mathrm{~d} x}=\frac{x \log _{\mathrm{e}} 2 x-\log _{\mathrm{e}} 2}{x} \end{array}$

Asked in: MHT CET 2023 (12 May Shift 2)

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