Answer
$$x \approx 28.9$$
Work Step by Step
$a = x$
$$x^2 = b^2 + c^2 - 2bc \space cos \space \theta$$ $$x = \sqrt {(21)^2 + (42)^2 - 2(21)(42) \space cos \space 39 ^o}$$ $$x \approx 28.9$$
Precalculus: Mathematics for Calculus, 7th Edition
by Stewart, James; Redlin, Lothar; Watson, Saleem
Published by
Brooks Cole
ISBN 10:
1305071751
ISBN 13:
978-1-30507-175-9
Chapter 6 - Section 6.6 - The Law of Cosines - 6.6 Exercises - Page 520: 3
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