# How do you find all local maximum and minimum points using the second derivative test given #y=cos^2x-sin^2x#?

##### 1 Answer

Dec 15, 2016

#### Explanation:

As:

we do not really need derivatives because we know that

However we can check:

so the critical points occur for:

and in fact:

#y''(2kpi) = -4 < 0# so these points are maximums, and

#y''((2k+1pi)) = 4 > 0# so these points are minimums.