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: 108

Answer

All are positive.

Work Step by Step

$-640^{\circ}+2\cdot360^{\circ}=80^{\circ}$ $80^{\circ}$ is coterminal with $-640^{\circ}$ and is in the first quadrant. In the first quadrant $x$, $y$, and $r$ are positive and therefore all of its trigonometric function values are positive.
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