Find all relative extrema in the function h(x)=cos(2pix/3) on the interval [0,2]
argument (2 pi x/3) = 0 to 4 pi/3 or zero to 240 degrees.
max at 0
min at 180
at 0, x = 0 and h(x) = 1
at 180 2 pi x/3 = pi so x = 3/2 and h = -1
max at 0
min at 180
at 0, x = 0 and h(x) = 1
at 180 2 pi x/3 = pi so x = 3/2 and h = -1