Question:
If $y=y(x)$ is the solution of the differential equation, $x \frac{\mathrm{d} y}{\mathrm{~d} x}+2 y=x^{2}$ satisfying $y(1)=1$, then $y\left(\frac{1}{2}\right)$ is equal to:
Correct Option: , 3
Solution:
Since, $x \frac{d y}{d x}+2 y=x^{2}$
$\Rightarrow \quad \frac{d y}{d x}+\frac{2}{x} y=x$
I.F. $\quad=e^{\int \frac{2}{x} d x}=e^{2 \ln x}=e^{\ln x^{2}}=x^{2}$.
Solution of differential equation is:
$y \cdot x^{2}=\int x \cdot x^{2} d x$
$y \cdot x^{2}=\frac{x^{4}}{4}+C$ ....(1)
$\because \quad y(1)=1$
$\therefore \quad C=\frac{3}{4}$
Then, from equation (1)
$y \cdot x^{2}=\frac{x^{4}}{4}+\frac{3}{4}$
$\therefore \quad y=\frac{x^{2}}{4}+\frac{3}{4 x^{2}}$
$\therefore \quad y\left(\frac{1}{2}\right)=\frac{1}{16}+3=\frac{49}{16}$