An integrating factor of the equation $\left(1+y+x^2 y\right) d x+\left(x+x^3\right) d y=0$ is

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

Solution

Given, differential equation is, $ \begin{aligned} & d x\left(1+y+x^2 y\right)+\left(x+x^3\right) d y=0 \\ \Rightarrow \quad & \frac{d y}{d x}=-\left[\frac{1+y+x^2 y}{x+x^3}\right] \end{aligned} $ $ \begin{aligned} & \Rightarrow \quad \frac{d y}{d x}=-\left\{\frac{1}{x\left(1+x^2\right)}+\frac{\left(1+x^2\right) y}{x\left(1+x^2\right)}\right\} \\ & \Rightarrow \quad \frac{d y}{d x}-\frac{y}{x}=-\frac{1}{x\left(1+x^2\right)} \\ & \end{aligned} $ Here, $p=-\frac{1}{2}, Q=-\frac{1}{x\left(1+x^2\right)}$ $ \begin{aligned} \text { Integrating factor } & \equiv e^{\int p d x} \\ & =e^{\int\left(-\frac{1}{x}\right)} d x \\ & =e^{-\log x} \\ & =e^{\log \left(\frac{1}{x}\right)} \\ & =\frac{1}{x} \end{aligned} $

Asked in: AP EAMCET 2013

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