solve the equation for the interval
0<x<2pie
cos^2 x + 2cosx + 1 = 0
cos^2 x + 2cosx + 1 = 0 factors to
(cos x + 1)^2 = 0
cos x + 1 = 0
cos x = -1
x = PI
0<x<2pie
cos^2 x + 2cosx + 1 = 0
(cos x + 1)^2 = 0
cos x + 1 = 0
cos x = -1
x = PI