Precalculus (6th Edition) Blitzer

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

Chapter 6 - Mid-Chapter Check Point - Page 756: 6

Answer

The solution is $A=28{}^\circ,B=42{}^\circ,\ \text{ and }\ C=110{}^\circ $.

Work Step by Step

The provided sides of the triangle are given below: $a=5.0,b=7.2,c=10.1$ Using the law of cosines, we will find the side b of the triangle. That is, ${{c}^{2}}={{a}^{2}}+{{b}^{2}}-2ab\,\cos \,C$ Therefore, $\begin{align} & \cos \,C=\frac{{{a}^{2}}+{{b}^{2}}-{{c}^{2}}}{2ab} \\ & \cos \,C=\frac{{{5}^{2}}+{{7.2}^{2}}-{{10.1}^{2}}}{2\times 5\times 7.2} \\ & \cos \,C=-0.3496 \end{align}$ Thus, $C=110{}^\circ $. Now, by using the law of sines we will find the angle A of the triangle. That is, $\begin{align} & \frac{\sin \,A}{a}=\frac{\sin \,C}{c} \\ & \frac{\sin \,A}{5}=\frac{\sin \,110{}^\circ }{10.1} \end{align}$ This implies that $\begin{align} & \sin \,A=5\times \frac{\sin \,110{}^\circ }{10.1} \\ & =0.4652 \end{align}$ This implies that $A=28{}^\circ $. Now the third angle will be found as below: $\begin{align} & B=180{}^\circ -A-C \\ & =180{}^\circ -28{}^\circ -110{}^\circ \\ & B=42{}^\circ \end{align}$ Therefore, the solution is $A=28{}^\circ,B=42{}^\circ,\ \text{ and }\ C=110{}^\circ $.
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