`y = 3cos(x), [0,2pi]` Find the absolute extrema of the function on the closed interval.
First find the critical x values of the function. To find the critical values, set the derivative equal to zero and solve for the x value(s).
Plug in the critical values and the endpoints of the closed interval in to the original function.
Examine the f(x) values.
The absolute maximum is at the points `(0,3) (2pi,3)`
The absolute minimum is at the point `(pi,-3)`