The coterminal angles of θ can be calculated using the formula:
[tex]\theta+2\pi n[/tex]Where n = 0, ±1, ±2, etc. In particular, for θ = 20π/3 and n = -3:
[tex]\begin{gathered} \frac{20\pi}{3}-2\pi\cdot3=\frac{20\pi-18\pi}{3} \\ \\ \therefore\frac{2\pi}{3}=120\degree \end{gathered}[/tex]