Question

What are all the exact solutions of cos x = - sqrt(3) / 2 on the interval pi <= x <= 2 pi ? Give your answer in radians.

A )pi / 6 and 11 pi /6

B ) 5 pi / 6

C ) 7 pi / 6

D ) 5 pi / 6 and 7 pi / 6

Answer 1

C. 7pi/6

Explanation:

hope this helps :)

Answer 2

Interval: pi <= x <= 2pi OR 180<= x <= 360

This means the interval must be between Quadrants 3/4

pi/6 = 30 degrees which is < 180

5pi/6 = 150 degrees which is < 180

7pi/6 = last option but = 210 degrees which is in Q3

cos (7pi/6) = - sqrt(3)/2

Ans: C