| written 7.8 years ago by | • modified 7.7 years ago |
$ x\frac{dy}{dx}=y-\frac{y^2}{x}\\ x\frac{dy}{dx}=\frac{xy-y^2}{x}$
$xdy=\frac{xy-y^2}{x}dx\\ x^2dy=(xy-y^2)dx$
$(xy-y^2)dx-x^2dy=0\\ M=xy-y^2 \\ N=-x^2$
$\frac{\partial M}{\partial y}=x-2y$
$ \frac{\partial N}{\partial x}=-2x$
$\frac{\partial M}{\partial y}\neq\frac{\partial M}{\partial y}$
The given Equation is not an exact differential equation.
M and N are homogenous functions of degree 3
$I.F=\frac{1}{Mx+Ny}$
$=\frac{1}{(xy-y^2)x-x^2y}$
$=\frac{1}{x^3y-y^2x-x^2y}$
$= \frac{1}{-yx^2}$
Multiplying the given equation by the integrating factor, we get
$ (xy-y^2)\left( \frac{1}{-y^2x}\right)dx-x^2\left( \frac{1}{-y^2x}\right)=0$
$ \left( \frac{1}{-y}+\frac{1}{x}\right)dx+\left( \frac{x}{-y^2}\right)dy=0$
$ \frac{\partial M}{\partial y}=\frac{1}{y^2}$
$ \frac{\partial N}{\partial x}=\frac{1}{y^2} $
The given Equation is an exact differential equation
Solution is given by
$\int Mdx+\int (Terms\ in\ N\ not\ containing\ x)dy=c$
$y=constant$
$ \int \left(\frac{-1}{y}+\frac{1}{x} \right)dx+\int 0dy=c$
$-\frac{x}{y}+\log x=c $

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