Let $y=y(x)$ be the solution of the differential equation $\frac{d y}{d x}+2 y=f(x)$, where $…

Let $y=y(x)$ be the solution of the differential equation $\frac{d y}{d x}+2 y=f(x)$, where $ f(x)=\left\{\begin{array}{lc} 1, & x \in[0,1] \\ 0, & \text { otherwise } \end{array}\right. $ If $y(0)=0$, then $y\left(\frac{3}{2}\right)$ is
  1. $\frac{e^2-1}{2 e^3}$
  2. $\frac{e^2-1}{e^3}$
  3. $\frac{1}{2 e}$
  4. $\frac{e^2+1}{2 e^4}$

Solution

When $x \in[0,1]$, then $\frac{d y}{d x}+2 y=1$ $ $ \begin{aligned} &\Rightarrow \mathrm{y}=\frac{1}{2}+C_1 e^{-2 x} \\ &\because y(0)=0 \Rightarrow y(x)=\frac{1}{2}-\frac{1}{2} e^{-2 x} \\ &\text { Here, } y(1)=\frac{1}{2}-\frac{1}{2} e^{-2}=\frac{e^2-1}{2 e^2} \end{aligned} $ $ When $x \notin[0,1]$, than $\frac{d y}{d x}+2 y=0$ $ $ \begin{gathered} \Rightarrow y=c_2 e^{-2 x} \\ \therefore y(1)=\frac{e^2-1}{2 e^2} \Rightarrow \frac{e^2-1}{2}=c^2 e^{-2} \Rightarrow C_2=\frac{e^2-1}{2} \\ \therefore y(x)\left(\frac{e^2-1}{2}\right) e^{-2 x} \Rightarrow y\left(\frac{3}{2}\right)=\frac{e^2-1}{2 e^3} \end{gathered} $ $

Asked in: JEE Main 2018 (15 Apr Shift 1 Online)

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