# Differential Equation Method OF UNDETERMINED COEFF

1. Oct 16, 2011

### FahimP

1. The problem statement, all variables and given/known data
I hav been trying to solve this differential equation by Method of Undetermined Coefficients for a long time.

y"-2y'-3y=-3te^(-t) ....................

We are supposed to guess a solution then differentiate and go from there. I guessed
y = (At + B)e^(-t) ............. but this does not work. ........... can someone help me on this ... I have also tried y = Ae^(-t) but this also doesnt work. Is it possible the book answer is wrong ?

2. Relevant equations

3. The attempt at a solution

2. Oct 16, 2011

### vela

Staff Emeritus
You first need to solve the homogeneous equation. What solution do you get to that?

3. Oct 16, 2011

### LCKurtz

Of course it's possible the book is wrong. It is also possible that you are wrong. You shouldn't have to "guess" what to try if you have the complementary solution.

I suggest you re-check your work for Ae-t. And if you get an answer you can always check it for yourself by plugging it into the DE.