### Question

**Find the principal solutions of the equation cos x = 1/2.**

A. π/3, 2π/3

B. 2π/3, 5π/3

C. π/3, 5π/3

D. π/6, 5π/6

**Answer: **C

**Solution:**

Since cos x is positive in 1st and 4th quadrant, so there are two principal solutions to above equation i.e. x = π/3, 2π-π/3.

So, **x = π/3, 5π/3.**