# Stuck on simple derivative, u(t)*t*e^(-5t), urnt?

1. Feb 18, 2006

### mr_coffee

Hello eveyrone, I think my brain just shut down, i'm confused on how i would take the derivative of this function i have circled below:

I know the chain rule, like if it was
t*e^(-5t) = e^(-5t) + t*(-5)e^(-5t)

2. Feb 18, 2006

### gulsen

$$(u_2 t e^{-7t})' = u_2' t e^{-7t} + u_2 (e^{-7t} + t (-7)e^{-7t})$$

3. Feb 18, 2006

### mr_coffee

Ahh thank u! I c it now!