# Using Laplace Transform to solve a differential equation

1. Nov 18, 2012

### november1992

1. The problem statement, all variables and given/known data

y" + y = 4δ(t-2π); y(0)=1, y'(0)=0

2. Relevant equations

L[f(t-a) U(t-a)] = $e^{-as}$ L[f(t)]

L[δ(t-c)] = $e^{-cs}$

3. The attempt at a solution

My answer is: cos(t) + 4U(t-2π)sin(t-2π).

When I used Wolframalpha it gave me 4sin(t)U(t-2π) + cos(t)

2. Nov 18, 2012

### I like Serena

Hi november1992!

Did you know that sin(t-2π)=sin(t) since the sine has a period of 2π?

3. Nov 18, 2012

### november1992

I meant to ask why is my answer different. I don't remember any of the trig identities so I'll have to review them.