Chapter 3 - Radian Measure and the Unit Circle - Section 3.1 Radian Measure - 3.1 Exercises - Page 105: 80

$-1$

Convert the angle measure to degrees to obtain: $=\pi \cdot \frac{180^o}{\pi} = 180^o$ Thus, $\sec{\pi} = \sec{180^o}$ 180 degrees is on the negative x-axis. From Section 1.3 (page 25) , we learned that: $\sec{180^o} = -1$ This means that: $\sec{\pi} = \sec{180^o} = -1$