Trigonometry
posted by Lindsey .
Find all solutions of the equation in the interval [0,2pi] algebraically.
sin^2x + cosx + 1 = 0

(1cos^2 x) + cos x + 1 = 0
 cos^2 x + cos x + 2 = 0
cos^2 x  cos x  2 = 0
(cos x  2)(cos x + 1) = 0
cos x = 2 impossible, out of range
so
cos x = 1
pi