Answer
$2cos^3~x-cos~x = \frac{cos^2~x-sin^2~x}{sec~x}$
Work Step by Step
$2cos^3~x-cos~x = (2cos^2~x-1)(cos~x)$
$2cos^3~x-cos~x = \frac{2cos^2~x-(sin^2~x+cos^2~x)}{\frac{1}{cos~x}}$
$2cos^3~x-cos~x = \frac{cos^2~x-sin^2~x}{sec~x}$
Trigonometry (10th Edition)
by Lial, Margaret L.; Hornsby, John; Schneider, David I.; Daniels, Callie
Published by
Pearson
ISBN 10:
0321671775
ISBN 13:
978-0-32167-177-6
Chapter 5 - Review Exercises - Page 243: 50
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