Question #343407

(x^3+y^3)=(3xy^2)dy/dx


1
Expert's answer
2022-05-23T23:18:42-0400

A Bernoulli differential equation


dydx13xy=x23y2\dfrac{dy}{dx}-\dfrac{1}{3x}y=\dfrac{x^2}{3}y^{-2}

Substitute

z=y1(2)=y3z=y^{1-(-2)}=y^3

dzdx=3y2dydx\dfrac{dz}{dx}=3y^2\dfrac{dy}{dx}

dydx=13y2dzdx\dfrac{dy}{dx}=\dfrac{1}{3y^2}\dfrac{dz}{dx}

Then


dzdx1xz=x2\dfrac{dz}{dx}-\dfrac{1}{x}z=x^2

IF=e(1/x)dx=1xIF=e^{\int (-1/x)dx}=\dfrac{1}{x}

1xdzdx1x2z=x\dfrac{1}{x}\dfrac{dz}{dx}-\dfrac{1}{x^2}z=x


ddx(zx)=x\dfrac{d}{dx}(\dfrac{z}{x})=x

zx=x22+C\dfrac{z}{x}=\dfrac{x^2}{2}+C

z=x32+Cxz=\dfrac{x^3}{2}+Cx

y3=x32+Cxy^3=\dfrac{x^3}{2}+Cx


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