Chapter 13, Trigonometric Ratios and Functions - 13.2 Define General Angles and Use Radian Measure - 13.2 Exercises - Skill Practice - Page 863: 19

$\dfrac{13\pi}{2}$ and $\dfrac{-3\pi}{2}$

a) Need to add $2 \pi$ to the given radian measurements. Thus, we have $\dfrac{9 \pi}{2}+2 \pi=\dfrac{9 \pi}{2}+\dfrac{4 \pi}{2}$ $=\dfrac{13\pi}{2}$ b) Need to subtract $6 \pi$ to the given radian measurements. Thus, we have $\dfrac{9 \pi}{2}-6 \pi=\dfrac{9 \pi}{2}-\dfrac{12 \pi}{2}$ $=\dfrac{-3\pi}{2}$