Q.
Let $x=x(y)$ be the solution of the differential equation $y^2\,dx+\left(x-\frac1y\right)dy=0$. If $x(1)=1$, then $x\left(\frac12\right)$ is:
A) $\frac12+e$
B) $3+e$
C) $3-e$
D) $\frac32+e$
Explanation
[Solution by Dr. Abubacker] $\frac{dx}{dy}+\frac{x}{y^2}=\frac1{y^3}$; the integrating factor is $e^{-1/y}$, giving $x=1+\frac1y+Ce^{1/y}$. $x(1)=1\Rightarrow C=-e^{-1}$, so $x(\tfrac12)=1+2-e=3-e$. Answer (3).
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.