The integrating factor of differential equation $\left(1+y+x^{2} y\right) d x+\left(x+x^{3}\right) d y=0$ is

The integrating factor of differential equation $\left(1+y+x^{2} y\right) d x+\left(x+x^{3}\right) d y=0$ is
  1. $\frac{1}{x}$
  2. $x$
  3. $\log x$
  4. $e^{x}$

Solution

We have $\left(1+y+x^{2} y\right) d x+\left(x+x^{3}\right) d y=0$ $\therefore \frac{d y}{d x}=\frac{-\left(1+y+x^{2} y\right)}{x\left(1+x^{2}\right)}=\frac{-\left[1+y\left(1+x^{2}\right)\right]}{x\left(1+x^{2}\right)}$ $\therefore \frac{d y}{d x}=\frac{-1}{x\left(1+x^{2}\right)}-\frac{y\left(1+x^{2}\right)}{x\left(1+x^{2}\right)}$ $\therefore \frac{d y}{d x}+\left(\frac{1}{x}\right) y=\frac{-1}{x\left(1+x^{2}\right)}$ $\therefore$ I.F. $=e^{\int \frac{1}{x} d x}=e^{\log x}=x$

Asked in: MHT CET 2020 (19 Oct Shift 1)

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