Let the solution $y=y(x)$ of the differential equation $\frac{\mathrm{d} y}{\mathrm{~d} x}-y=1+4 \sin x$ satisfy $y(\pi)=1$. Then $y\left(\frac{\pi}{2}\right)+10$ is equal to __________.
Answer (integer)
7
Solution
<p>$$\begin{aligned}
& \frac{d y}{d x}-y=1+4 \sin x \\
& \text { Integrating factor }=e^{-\int d x}=e^{-x}
\end{aligned}$$</p>
<p>Solution is $y e^{-x}=\int(1+4 \sin x) e^{-x} d x$</p>
<p>$$\begin{aligned}
& =-e^{-x}+2 \cdot e^{-x}(-\sin x-\cos x)+C \\
y(\pi) & =1 \Rightarrow C=0
\end{aligned}$$</p>
<p>Hence $y(x)=-1-2(\sin x+\cos x)$</p>
<p>$y\left(\frac{\pi}{2}\right)+10=7$</p>
About this question
Subject: Mathematics · Chapter: Differential Equations · Topic: Order and Degree
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