rolle's theorem

f must be continuous on a closed interval [a,b]

differential on (a,b) with f(a)=f(b)

Then, there is atleast one point C in (a,b) such that f'(c)=0

I am suppose to determine if rolle's theorem applies to the fuction and solve

in the inverval [-1,1]

Mathab says the assumptions for the Theorem have not been satisfied. I am under the impression they are satisfied. I was wonderifing if someone could provide and explanation as to why the theorem has not been satisfied.