Chapter 3 - Radian Measure and the Unit Circle - Section 3.1 Radian Measure - 3.1 Exercises - Page 105: 89

$3\pi$; $-\pi$

Coterminal angles differ by a multiple of $2\pi$ radians. So, we can add $2\pi$ radians to get a positive angle that is coterminal with $\pi$ radians. $\pi+2\pi=3\pi$ We can subtract $2\pi$ radians to get a negative angle that is coterminal with $\pi$ radians. $\pi-2\pi=-\pi$