[tex]a) \\ 45 ^{\circ} = 45 ^{\circ} \times \frac{\pi}{180} = \frac{\pi}{4} [/tex]
[tex]b) \\ 30^{\circ} = 30^{\circ} \times \frac{\pi}{180} = \frac{\pi}{6} [/tex]
[tex]c) \\ 90^{\circ} = 90^{\circ} \times \frac{\pi}{180} = \frac{\pi}{2} \\ [/tex]
[tex]d) \\ 120^{\circ} = 120^{\circ} \times \frac{\pi}{180} = \frac{2\pi}{3} [/tex]
