Calculus (3rd Edition)

Published by W. H. Freeman
ISBN 10: 1464125260
ISBN 13: 978-1-46412-526-3

Chapter 1 - Precalculus Review - 1.4 Trigonometric Functions - Preliminary Questions - Page 29: 4



Work Step by Step

Since the sum of the interior angles of a triangle is $180$, then in a right triangle any other angle $\theta$ should satisfy $$0\lt\theta\lt \pi/2$$ so the right answer is (a).
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