Precalculus (6th Edition)

Published by Pearson
ISBN 10: 013421742X
ISBN 13: 978-0-13421-742-0

Chapter 5 - Trigonometric Functions - 5.2 Trigonometric Functions - 5.2 Exercises - Page 519: 103

Answer

Cosine and secant are positive. All others are negative.

Work Step by Step

A $-80^{\circ}$ is in quadrant IV. In the fourth quadrant, $x$ and $r$ are positive but $y$ is negative. $\implies \sin\theta=\frac{y}{r}=\text{negative}$ As $\csc\theta=\frac{1}{\sin\theta}$, $\csc\theta$ is also negative. $\cos\theta=\frac{x}{r}=\text{positive}$ Secant which is the inverse of cosine is also positive. $\tan\theta=\frac{y}{x}=\text{negative}$ $\cot\theta=\frac{x}{y}=\text{negative}$
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