Use reference angles or the symmetry shown in Figure 59 to obtain:
(a) \(\sin \dfrac{7\pi }{4}=-\dfrac{\displaystyle\sqrt{2}}{2}\)
(b) \(\cos \dfrac{7\pi }{6}=-\dfrac{\displaystyle\sqrt{3}}{2}\)
(c) \(\tan \dfrac{2\pi }{3}=\dfrac{\dfrac{\displaystyle\sqrt{3}}{2}}{-\dfrac{1}{2}}=-\displaystyle\sqrt{3}\)
(d) \(\cos \left( -\dfrac{3\pi }{4}\right) =-\dfrac{\displaystyle\sqrt{2}}{2}\)
(e) \(\sin \left( -\dfrac{\pi }{6}\right) =-\dfrac{1}{2}\)
(f) \(\sin \dfrac{7\pi }{3}=\dfrac{\displaystyle\sqrt{3}}{2}\)