Calculus Question

Question

Find the solution set of 2 cos² x = 1/2 in the interval 0 ≤ x < 2π , or when a table or calculator is used, in the interval 0° ≤ x < 360°.

What is the second from the last step?

a. cos x = 1/2

b. cos x = ± 1/2

c. cos x = ± 1

d. cos x = 1

My answer was a

What are the answers?

a. π/6 , 5π/6 , 7π/6 , 11π/6

b. π/6 and 5π/6

c. π/3 and 5π/6

d. π/3 , 2π/3 , 4π/3 , 5π/3

My answer was d

Answer 1

2 cos²x = ½

cos²x = ¼

cos x = ± ½ (Remember the ±.)

x = π/3, 2π/3, 4π/3, 5π/3