EXAMPLE 4
Use
reference angles to evaluate functions
Evaluate (a) tan ( – 240°) and (b) csc
.
17π
6
SOLUTION
tan (–240°) = – tan 60° = –
√
3
a.
The angle – 240° is coterminal with 120°. The reference angle is θ' =
180° – 120° = 60°. The tangent function is negative in Quadrant II, so you can write: