Trigonometry (10th Edition)

Published by Pearson
ISBN 10: 0321671775
ISBN 13: 978-0-32167-177-6

Chapter 1 - Trigonometric Functions - Section 1.4 Using the Definitions of the Trigonometric Functions - 1.4 Exercises: 85



Work Step by Step

If initial angle $90^{\circ}\leq\theta\leq 180^{\circ}$, then the double angle will be $180^{\circ}\leq2\theta\leq 360^{\circ}$. In this range the y is negative therefore the sine will be negative (remember that r is always positive)
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