Trigonometry (11th Edition) Clone

Recall: (1) An angle and its reference angle either have the same trigonometric function values or differ only in signs. (2) $\tan{\theta} = \dfrac{y}{x}$ $\frac{3\pi}{2}$ is a special angle whose terminal side is the negative y-axis.. Note that the negative y-axis intersects the unit circle at the point $(0, -1)$. Therefore, $\tan{(\frac{3\pi}{2})}=\frac{-1}{0}$, which is undefined.