ODE5.2

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y'+xy=xy^2\,

A Bernoulli Equation has the form

y'+p(x)y=q(x)y^n\,

And for these types of DE's a substitution of z = y^{1-n}\, is recommended. In the present problem, n=2\, and so

z = y^{-1}\,

y = z^{-1}\,

y' = -\frac{z'}{z^2}\,

Substituting these new variables into the original equation,

-\frac{z'}{z^2} + \frac{x}{z} = \frac{x}{z^2}\,

z'-xz=-x\,

Use the integrating factor e^{\int -x dx} = e^{-x^2/2}\,

e^{-x^2/2}z' - e^{-x^2/2}xz = -e^{-x^2/2}x\,

\frac{d}{dx}[ e^{-x^2/2} z ] = -e^{-x^2/2}x\,

e^{-x^2/2} z = e^{-x^2/2} + c_1\,

z = 1+c_1e^{x^2/2}\,

Undoing the substitution z = y − 1,

y^{-1} = 1+c_1e^{x^2/2}\,

y = (1+c_1e^{x^2/2})^{-1}\,

Ordinary Differential Equations

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