# Math Help - Undet. Coefficients

1. ## Undet. Coefficients

Using undetermined coefficients, find the gen. sol'n of the following Dif EQ:

$y'' + 4y' + 9y = 18t^2 + 1$

So, I'm not exactly sure how I'd do this. I was thinking of solving the homogenous part, and then the particular, but I think this is variation of parameters.

2. $Y_{p}(t) = At^2 + Bt + C$. Then differentiate. So $2A + 4 \left(2At + B \right) + 9 \left(At^2 + Bt + C \right) = 18t^2 + 1$. Expand out, write in decreasing powers, the solve for coefficients.