The solution of the differential equation $(1+x) y \mathrm{~d} x+(1-y) x \mathrm{~d} y=0$ is

The solution of the differential equation $(1+x) y \mathrm{~d} x+(1-y) x \mathrm{~d} y=0$ is
  1. $\log x y-x+y=C$
  2. $\log \left(\frac{x}{y}\right)-x+y=C$
  3. $\log x y-x-y=C$
  4. $\log (x y)+x-y=C$

Solution

$\begin{aligned} & (1+x) y \mathrm{~d} x+(1-y) x \mathrm{~d} y=0 \\ & \Rightarrow \int \frac{1+x}{x} \mathrm{~d} x=\int \frac{y-1}{y} \mathrm{~d} y \\ & \Rightarrow \log |x|+x=y-\log |y|+C \\ & \Rightarrow \log (x y)+x-y=C\end{aligned}$

Asked in: MHT CET 2022 (10 Aug Shift 2)

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