Find all numbers c that satisfy the conclusion of the mean value theorem for the following function and interval:$$f(x)=3x^2+2x+2 \tag{[-1,1]}$$so far I have $$f'(x)=6x+2$$$$6x+2=-1$$$$x=-1/2$$and$$6x+2=1$$$$x=-\frac{1}{6}$$I know both of these are wrong, and the written answer is 0, but I don't see how to get the correct answer.