Question

Se cos2 x = 1 e 0 < x < 2π, então, necessariamente,
A) sen x=0
B) x=pi/3
C) sen x < 0
D) x=4pi/3
E) sen x = -1

Answer 1

cos2x = 1=> cos²x - sen²x = 1
1-sen²x - sen²x = 1
-2se²x = 1 - 1
sen²x = 0
senx = 0

Letra A