Medium INTEGER +4 / -1 PYQ · JEE Mains 2024

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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