Chapter 6 - The Circular Functions and Their Graphs - Chapter 6 Test Prep - Review Exercises - Page 644: 5

$$\frac{\pi }{4}{\text{radian}}$$

$$\eqalign{ & {45^ \circ } \cr & {\text{Multiply by }}\frac{\pi }{{180}}{\text{radian}} \cr & {45^ \circ } = 45\left( {\frac{\pi }{{180}}{\text{radian}}} \right) \cr & {45^ \circ } = \frac{{45\pi }}{{180}}{\text{radian}} \cr & {\text{Simplify}} \cr & {45^ \circ } = \frac{\pi }{4}{\text{radian}} \cr} $$