# Nonhomogenous 2nd order DE

1. Mar 9, 2008

### jesuslovesu

1. The problem statement, all variables and given/known data
Well I've got another one that totally sucks.
$$y'' + 2y' + 5y = 4e^{-t}cos(2t)$$

2. Relevant equations

3. The attempt at a solution

I tried Y(t) = $$Ae^{-t}cos(2t) + Be^{-t}sin(2t)$$ but that unfortunately yielded $$0 = 4e^{-t} cos(2t)$$

So my question is how does one modify Y(t) in this type of situation? The only thing I can think of is something like $$Y(t) = Ae^{-t}t^2cos(2t) + Be^{-t}tsin(2t)$$ but that seems rather painful

2. Mar 9, 2008

### Dick

Try,
$$Y(t) = Ae^{-t}tcos(2t) + Be^{-t}tsin(2t)$$
which is what you wrote down but I changed a t^2 to a t. Yeah, it's kind of painful, but it will work. Without the t's it just the homogeneous solution. You knew that would give you zero, right?

Last edited: Mar 9, 2008