Precalculus (6th Edition) Blitzer

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

Chapter 5 - Section 5.4 - Product-to-Sum and Sum-to-Product Formulas - Exercise Set - Page 691: 54

Answer

The given statement makes sense.

Work Step by Step

One of the product-to-sum formulas is $\sin \alpha \cos \beta =\frac{1}{2}\left[ \sin \left( \alpha +\beta \right)+\sin \left( \alpha -\beta \right) \right]$. Therefore, according to the above-mentioned formula, the value of $\alpha $ is ${{13}^{\circ }}$ and the value of $\beta $ is ${{48}^{\circ }}$. Thus, the expression can be evaluated as: $\begin{align} & \sin {{13}^{\circ }}\cos {{48}^{\circ }}=\frac{1}{2}\left[ \sin \left( {{13}^{\circ }}+{{48}^{\circ }} \right)+\sin \left( {{13}^{\circ }}-{{48}^{\circ }} \right) \right] \\ & =\frac{1}{2}\left[ \sin {{61}^{\circ }}+\sin \left( -{{35}^{\circ }} \right) \right] \end{align}$ Now, applying the even-odd identity, which is $sin(-x)=-\sin x$, the expression can be further evaluated as shown below: $\frac{1}{2}\left[ \sin {{61}^{\circ }}+\sin \left( -{{35}^{\circ }} \right) \right]=\frac{1}{2}\left( \sin {{61}^{\circ }}-\sin {{35}^{\circ }} \right)$ Therefore, $\sin {{13}^{\circ }}cos{{48}^{\circ }}$ can be expressed as $\frac{1}{2}\left( \sin {{61}^{\circ }}-\sin {{35}^{\circ }} \right)$.
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