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Question Number 181218 by Mastermind last updated on 23/Nov/22

Solve the Differential equation:  x(dy/dx)−y=2y(lnx−lny)    .

$$\mathrm{Solve}\:\mathrm{the}\:\mathrm{Differential}\:\mathrm{equation}: \\ $$$$\mathrm{x}\frac{\mathrm{dy}}{\mathrm{dx}}−\mathrm{y}=\mathrm{2y}\left(\mathrm{lnx}−\mathrm{lny}\right) \\ $$$$ \\ $$$$. \\ $$

Answered by qaz last updated on 23/Nov/22

y=zx  x(dy/dx)−y=x((xdz+zdx)/dx)−zx=−2zxlnz  ⇒(dz/(zlnz))=−(2/x)dx  ⇒lnz=Cx^(−2)   ⇒z=e^(Cx^(−2) )   ⇒y=xe^(Cx^(−2) )

$${y}={zx} \\ $$$${x}\frac{{dy}}{{dx}}−{y}={x}\frac{{xdz}+{zdx}}{{dx}}−{zx}=−\mathrm{2}{zxlnz} \\ $$$$\Rightarrow\frac{{dz}}{{zlnz}}=−\frac{\mathrm{2}}{{x}}{dx} \\ $$$$\Rightarrow{lnz}={Cx}^{−\mathrm{2}} \\ $$$$\Rightarrow{z}={e}^{{Cx}^{−\mathrm{2}} } \\ $$$$\Rightarrow{y}={xe}^{{Cx}^{−\mathrm{2}} } \\ $$

Commented by universe last updated on 23/Nov/22

good solution sir

$${good}\:{solution}\:{sir} \\ $$

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