Resposta :
Cosx + 1 = 1 - cos^2x
cos^2x + cosx = 0
cosx (cosx + 1) = 0
cosx = 0
cosx = -1
S={pi/2, pi, 3pi/2}
cos^2x + cosx = 0
cosx (cosx + 1) = 0
cosx = 0
cosx = -1
S={pi/2, pi, 3pi/2}