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Solve $\frac{dy}{dx}=xy+y^2e^{{{-x}^2}/2}logx$ .
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| written 7.8 years ago by | • modified 7.7 years ago |
$ \frac{dy}{dx}=xy+y^2e^{-\frac{x^2}{2}}\log x$
Dividing throughout by $y^2$,we get
$\frac{1}{y^2}\frac{dy}{dx}-\frac{1}{y}x=e^{-\frac{x^2}{2}\log x} $ $\dots\dots(1)$
put
$\frac{-1}{y}=v$
$ \frac{1}{y^2}\frac{dy}{dx}=\frac{dv}{dx}$
Eqn(1)becomes
$ \frac{dv}{dx}+xv=e^{-\frac{x^2}{2}\log x} $
This is a linear differential equation in $v $with $P=x$ and $Q=e^{-\frac{x^2}{2}}\log x$
$I.F=e^{\int xdx}=e^{\frac{x^2}{2}} $
The solution is
$ve^{\frac{x^2}{2}}=\int e^{\frac{x^2}{2}}e^{\frac{-x^2}{2}}\log xdx+c$
$ ve^{\frac{x^2}{2}}=\int \log xdx+c$
$e^{\frac{x^2}{2}}=\log x.x-\int x.\frac{1}{x}dx+c$
$ve^{\frac{x^2}{2}}=\log x.x-x+c$
$ -\frac{1}{y}e^{\frac{x^2}{2}}=x(\log x-1)+c$
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