Question

Calcule o cosseno de 2x sendo o cosseno de x igual a 1/2

Answer 1

Cos x = 1/2 => x= 60° 

cos 2x = 2 cos² x - 1

cos 2x = cos 120° = 2 cos² 60 - 1 = 2 (1/2)² - 1 = (2 x 1/4) - 1 = 1/2 - 1 

cos 2x = cos 120° = - 1/2