Answer
a. $\frac{5\pi}{4}$.
b. See figure.
c. $\frac{\pi}{4}$
Work Step by Step
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)
