## Elementary Geometry for College Students (6th Edition)

the identity cot α = $\frac{cos α}{sin α}$ is valid
cot α = $\frac{b}{a}$ cos α = $\frac{b}{c}$ ; sin α = $\frac{a}{c}$ $\frac{cos α}{sin α}$ = $\frac{\frac{b}{c}}{\frac{a}{c}}$= $\frac{b}{a}$ So cot α and $\frac{cos α}{sin α}$ are equivalent