# Math Help - another differential equation

1. ## another differential equation

(dy/dt) + y = cos (e^t)??? how???

2. Originally Posted by crafty
(dy/dt) + y = cos (e^t)??? how???
Integrating factor

$\mu = e^t$

so

$\frac{d}{dt} \left( e^t y \right) = e^t \cos e^t$

$\int d \left( e^t y \right) = \int e^t \cos e^t\, dt + c$

I trust you can do the rest.