For $x>1$, if $(2 x)^{2 y}=4 e^{2 x-2 y}$, then $(1+\log 2 x)^2 \frac{d y}{d x}$ is equal to

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

Solution

$\begin{aligned} & (2 x)^{2 y}=4 e^{2 x-2 y} \Rightarrow 2 y \log (2 x)=\log 4+2 x-2 y \\ & \Rightarrow 2 y \log (2 x)=2 \log 2+2 x-2 y\end{aligned}$ Different w.r.t $x$ $\begin{aligned} & \frac{d y}{d x} \cdot \log (2 x)+y \cdot \frac{1}{2 x} \cdot 2=0+1-\frac{d y}{d x} \\ & \Rightarrow \frac{d y}{d x}(1+\log 2 x)=1-\frac{y}{x}=1-\frac{x+\log 2}{x(1+\log 2 x)} \\ & {\left[\because \text { from }(1) y=\frac{x+\log 2}{(1+\log 2 x)}\right]} \\ & \Rightarrow \frac{d y}{d x}(1+\log 2 x)^2=\frac{x(1+\log 2 x)-x-\log 2}{x} \\ & \Rightarrow(1+\log 2 x)^2=\frac{d y}{d x}=\frac{x \log 2 x-\log 2}{x}\end{aligned}$

Asked in: MHT CET 2022 (06 Aug Shift 1)

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