Question

Solve this multiple-angle equation.

cos x/2 = -(sqrt3)/2

Answer 1

well, you know that cos π/6 = √3/2
So, with the negative value, you have

x/2 = 5π/6 or 7π/6

Answer 2

So the solutions are also 5π/6 + 2npi and 7π/6 2npi, right?

Answer 3

nope. cos(x/2) has period 4π

Answer 4

also, note that x/2 = 5π/6. So, x = 5π/3.
Watch the details, guy.