Find the general solution of the given differential equation. x2y' + x(x + 2)y = ex y(x) = Give the largest interval over which the general solution is defined. (Think about the implications of any singular points. Enter your answer using interval notation.) Determine whether there are any transient terms in the general solution. (Enter the transient terms as a comma-separated list; if there are none, enter NONE.)

Respuesta :

Multiply both sides of the ODE by [tex]e^x[/tex]:

[tex]x^2y'+x(x+2)y=e^x\implies x^2e^xy'+(x^2+2x)e^xy=e^{2x}[/tex]

and notice that [tex](x^2e^x)'=2xe^x+x^2e^x=(x^2+2x)e^x[/tex]. So we can collapse the left side and write it as the derivative of a product:

[tex]\left(x^2e^xy\right)'=e^{2x}[/tex]

[tex]\implies x^2e^xy=\displaystyle\int e^{2x}\,\mathrm dx[/tex]

[tex]\implies x^2e^xy=\dfrac{e^{2x}}2+C[/tex]

[tex]\implies y=\dfrac{e^x}{2x^2}+\dfrac C{x^2e^x}[/tex]

We can't have [tex]x=0[/tex], so [tex](0,\infty)[/tex] (or [tex](-\infty,0)[/tex], depending on the initial value) would be the largest interval over which the solution is valid.

As [tex]x\to\infty[/tex], we see the [tex]\dfrac C{x^2e^x}[/tex] term rapidly approaching 0, so this is the only transient term.