Precalculus (6th Edition) Blitzer

Published by Pearson
ISBN 10: 0-13446-914-3
ISBN 13: 978-0-13446-914-0

Chapter 5 - Section 5.1 - Verifying Trigonometric Identities - Exercise Set - Page 660: 73

Answer

The expression in terms of the function $\sec x\ \text{ and }\ \tan x$ is $\sec x\tan x$.

Work Step by Step

By using the reciprocal identity of trigonometry $cscx=\frac{1}{sinx}$. And the above expression can be further solved as, $\begin{align} & \frac{1}{\csc x-\sin x}=\frac{1}{\frac{1}{\sin x}-\sin x} \\ & =\frac{1}{\frac{1-{{\sin }^{2}}x}{\sin x}} \end{align}$ Apply the Pythagorean identity of trigonometry ${{\sin }^{2}}x+{{\cos }^{2}}x=1$. Now, the expression ${{\cos }^{2}}x$ can be written as $1-{{\sin }^{2}}x$. so, $\frac{1}{\frac{1-{{\sin }^{2}}x}{\sin x}}=\frac{1}{\frac{{{\cos }^{2}}x}{\sin x}}$ Then, rewrite the main fraction bar as $\frac{1}{\frac{{{\cos }^{2}}x}{\sin x}}=1\div \frac{{{\cos }^{2}}x}{\sin x}$ Invert the divisor and multiply; then, we get: $1\div \frac{{{\cos }^{2}}x}{\sin x}=1\times \frac{\sin x}{{{\cos }^{2}}x}$ And the above expression is simplified as, $1\times \frac{\sin x}{{{\cos }^{2}}x}=\frac{1}{\cos x}\times \frac{\sin x}{\cos x}$ Now, apply the reciprocal identity of trigonometry $\sec x=\frac{1}{\cos x}$ , and the quotient identity of trigonometry $\tan x=\frac{\sin x}{\cos x}$. And the above expression can be further solved as, $\begin{align} & \frac{1}{\cos x}\times \frac{\sin x}{\cos x}=\sec x\times \tan x \\ & =\sec x\tan x \end{align}$ Thus, the given expression is written in the terms of the function $\sec x\ \text{ and }\ \tan x$ as $\sec x\tan x$. Hence, the expression $\frac{1}{\csc x-\sin x}$ in terms of the function $\sec x\ \text{ and }\ \tan x$ is $\sec x\tan x$.
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