## Trigonometry (11th Edition) Clone

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Recall: (1) An angle and its reference angle either have the same trigonometric function values or differ only in signs. (2) In a unit circle, $\cos{\theta} = x$ $\frac{3\pi}{2}$ 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, $\cos{\frac{3\pi}{2}} = 0$