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 543: 51

Answer

As left side transforms into right side, hence given identity- $ \frac{(\sin x + \cos x)^{2}}{\sin^{2} x - \cos^{2} x}$ = $ \frac{\sin^{2} x - \cos^{2} x}{(\sin x - \cos x)^{2}}$ is verified as true.

Work Step by Step

Given identity is- $ \frac{(\sin x + \cos x)^{2}}{\sin^{2} x - \cos^{2} x}$ = $ \frac{\sin^{2} x - \cos^{2} x}{(\sin x - \cos x)^{2}}$ Taking L.S. $ \frac{(\sin x + \cos x)^{2}}{\sin^{2} x - \cos^{2} x}$ = $ \frac{(\sin x + \cos x)^{2}}{(\sin x - \cos x) (\sin x + \cos x)}$ {Recall $a^{2} - b^{2}$ = (a-b)(a+b)} = $ \frac{(\sin x + \cos x)}{(\sin x - \cos x)}$ = $ \frac{(\sin x + \cos x)}{(\sin x - \cos x)}. \frac{(\sin x - \cos x)}{(\sin x - \cos x)}$ {Multiplying the numerator and denominator both by, $(\sin x - \cos x)$} = $ \frac{\sin^{2} x - \cos^{2} x}{(\sin x - \cos x)^{2}}$ {Recall $(a+b)(a-b) $ = $a^{2} - b^{2}$ } = R.S. As left side transforms into right side, hence given identity- $ \frac{(\sin x + \cos x)^{2}}{\sin^{2} x - \cos^{2} x}$ = $ \frac{\sin^{2} x - \cos^{2} x}{(\sin x - \cos x)^{2}}$ is verified as true.
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