If $y=y(x)$ is the solution of the differential equation $\frac{\mathrm{d} y}{\mathrm{~d} x}+2 y=\sin (2 x), y(0)=\frac{3}{4}$, then $y\left(\frac{\pi}{8}\right)$ is equal to :
Solution
<p>$$\begin{aligned}
& \frac{d y}{d x}+2 y=\sin 2 x \\
& \text { IF }=e^{2 d x}=e^{2 x} \\
& y \cdot e^{2 x}=\int e^{2 x} \sin 2 x d x+c \\
& =\frac{e^{2 x}}{8}(2 \sin 2 x-2 \cos 2 x)+c \\
& y(0)=\frac{3}{4} \\
& \frac{3}{4}=\frac{1}{8}(-2)+c \Rightarrow c=1 \\
& \text { Put } x=\frac{\pi}{8} \\
& y=\frac{1}{8} \times 2\left(\frac{1}{\sqrt{2}}-\frac{1}{\sqrt{2}}\right)+e^{-\pi / 4} \\
& y=e^{-\pi / 4}
\end{aligned}$$</p>
About this question
Subject: Mathematics · Chapter: Differential Equations · Topic: Order and Degree
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