



so the characteristic solution is

As a guess for the particular solution, let's back up a bit. The reason the choice of

works for the characteristic solution is that, in the background, we're employing the substitution

, so that

is getting replaced with a new function

. Differentiating yields


Now the ODE in terms of

is linear with constant coefficients, since the coefficients

and

will cancel, resulting in the ODE

Of coursesin, the characteristic equation will be

, which leads to solutions

, as before.
Now that we have two linearly independent solutions, we can easily find more via variation of parameters. If

are the solutions to the characteristic equation of the ODE in terms of

, then we can find another of the form

where


where

is the Wronskian of the two characteristic solutions. We have






and recalling that

, we have