Precalculus (6th Edition)

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

Chapter 6 - The Circular Functions and Their Graphs - 6.2 The Unit Circle and Circular Functions - 6.2 Exercises - Page 589: 58



Work Step by Step

A negative angle means the measurement is taken by moving clockwise from the positive x-axis. Note that the negative y-axis is $\frac{\pi}{2}$ radians (or $1.57$ radians) clockwise from the positive x-axis. This means that the angle $-1$ radians is in Quadrant IV. With $\sin{\theta}=y$, and since $y$ is negative in Quadrant IV, then $\sin{(-1)}$ must be negative.
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