## Trigonometry (11th Edition) Clone

$\sin{\frac{3\pi}{4}} = \frac{\sqrt2}{2}$
Recall: (1) An angle and its reference angle either have the same trigonometric function values or differ only in signs. (2) $\frac{\pi}{4}$ is a special angle whose sine value is known to be $\frac{\sqrt2}{2}$. Note that the reference angle of $\frac{3\pi}{4}$ is $\frac{\pi}{4}$. However, since $\frac{3\pi}{4}$ is in Quadrant II, then its sine value is also positive. Therefore, $\sin{\frac{3\pi}{4}} = \frac{\sqrt2}{2}$