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SSC Pure Mathematics QUESTION #11186
Question 1
The solution of $y' = \dfrac{x+y}{x}$ is:
  • $y = x\ln|kx|$✔️
  • $y = x\ln|x|$
  • $y = x\ln|kx|$
  • $y = \ln|x| + k$
Correct Answer Explanation
Rewrite: $y' = 1 + y/x$. This is homogeneous. Let $v = y/x$, so $y = vx$, $y' = v + xv'$. Then $v + xv' = 1+v \Rightarrow xv' = 1 \Rightarrow v' = 1/x \Rightarrow v = \ln|x| + C$. Therefore $y = vx = x(\ln|x|+C) = x\ln|x| + Cx = x\ln|kx|$ where $k = e^C$.