Solve 2cos2x - 1 = 0 for 0° < x < 360°

Question

Select your answer from the choices below:

A) 45°, 315°

B) 45°, 135°

C) 45°, 135°, 225°, 315°

D) 45°, 225°

Answer 1

NO

 

isolating the cosine:

cos2x = 1/2

cosine function is 1/2 when the angle is 60.
Cosine is positive in quadrants 1 and 4

The angles are 60 and 360-60 = 300

2x = 60 ---> x = 30

2x = 300 ---> x = 150