JEE MAIN - Mathematics (2024 - 4th April Morning Shift - No. 21)
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
7
Explanation
$$\begin{aligned} & \frac{d y}{d x}-y=1+4 \sin x \\ & \text { Integrating factor }=e^{-\int d x}=e^{-x} \end{aligned}$$
Solution is $$y e^{-x}=\int(1+4 \sin x) e^{-x} d x$$
$$\begin{aligned} & =-e^{-x}+2 \cdot e^{-x}(-\sin x-\cos x)+C \\ y(\pi) & =1 \Rightarrow C=0 \end{aligned}$$
Hence $$y(x)=-1-2(\sin x+\cos x)$$
$$y\left(\frac{\pi}{2}\right)+10=7$$
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