## Precalculus (6th Edition) Blitzer

a. $\frac{5\pi}{4}$. b. See figure. c. $\frac{\pi}{4}$
a. Given the angle $-\frac{19\pi}{4}=-\frac{24\pi-5\pi}{4}=-6\pi+\frac{5\pi}{4}$, we see that the positive angle that is less than $2\pi$ and is co-terminal with the given angle is $\frac{5\pi}{4}$. b. See figure. c. The reference angle can be found as $\frac{5\pi}{4}-\pi=\frac{\pi}{4}$ (angle with respect to the x-axis)