Trigonometry calculation

Question

Find the angles 0°<x<360° Cos(3x)=1

Answer 1

cos(3x) = 1

3x = k(360°), where k = 0, , -1, 2, -2, ...

x = k(120°)

If k = 1, x = 120°

If k = 2, x = 240°

Answer 2

cos 3x = 1

3x = 0

x = ?