Precalculus: Mathematics for Calculus, 7th Edition

Published by Brooks Cole
ISBN 10: 1305071751
ISBN 13: 978-1-30507-175-9

Chapter 7 - Section 7.1 - Trigonometric Identities - 7.1 Exercises - Page 544: 75

Answer

$\dfrac{\sin^{3}x+\cos^{3}x}{\sin x+\cos x}=1-\sin x\cos x$

Work Step by Step

$\dfrac{\sin^{3}x+\cos^{3}x}{\sin x+\cos x}=1-\sin x\cos x$ Factor the numerator and simplify: $\dfrac{(\sin x+\cos x)(\sin^{2}x-\sin x\cos x+\cos^{2}x)}{\sin x+\cos x}=1-\sin x\cos x$ $\sin^{2}x-\sin x\cos x+\cos^{2}x=1-\sin x\cos x$ Since $\sin^{2}x+\cos^{2}x=1$, the identity is proved: $1-\sin x\cos x=1-\sin x\cos x$
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