| written 7.8 years ago by | • modified 7.7 years ago |
$M=xy^3+y $
$ N=2(x^2y^2+x+y^4) $
$\frac{\partial{M}}{\partial{y}}=3xy^2+1$
$\frac{\partial{N}}{\partial{x}}=2(2xy^2+1)$
$\frac{\partial{M}}{\partial{y}}\neq \frac{\partial{N}}{\partial{x}}$
The given Equation is not an exact differential equation.
$\frac{\frac{\partial{N}}{\partial{x}}-\frac{\partial{M}}{\partial{y}}}{M} =\frac{2(2xy^2+1)-(3xy^2+1)}{xy^3+y} $
$=\frac{(4xy^2+4)-3xy^2-1}{xy^3+y}$
$=\frac{xy^2+1}{xy^3+y} =\frac{xy^2+1}{(xy^2+1)y} =\frac{1}{y}=f(y)$
$ I.F=e^{\int \frac{1}{y}dy}=e^{\log y}=y$
Multiplying the given equation by the integrating factor, we get
$(xy^3+y)y+2(x^2y^2+x+y^4)y=0$
$(xy^4+y^2)dx+2(x^2y^3+xy+y^5)dy=0$
$\frac{\partial{M}}{\partial{y}}=4xy^3+2y$
$\frac{\partial{N}}{\partial{x}}=2(2xy^3+y)=4xy^3+2y$$
The given Equation is an exact differential equation
Solution is given by
$\int Mdx+\int (Terms\ in\ N\ not\ containing\ x)dy=0$
$y=constant\\ \int (xy^4+y^2)dx-\int 2(y^5)dy=c$
$\frac{x^2y^4}{2}+xy^2-\frac{2y^6}{6}=c$
$\frac{x^2y^4}{2}+xy^2-\frac{y^6}{3}=c $

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