# Thread: 2nd derivative test

1. ## 2nd derivative test

I am having trouble with this problem :

use the second derivative test to find all relative extrema of f(x)=2sin(x)+cos(2x)

I differentiated and got to 2cos(x)-2sin(2x)

what should I do next?

2. You'll need the second derivative to see whether a given extremum is a max or a min. So take the second derivative.