Precalculus (6th Edition)

Published by Pearson
ISBN 10: 013421742X
ISBN 13: 978-0-13421-742-0

Chapter 8 - Application of Trigonometry - 8.2 The Law of Cosines - 8.2 Exercises - Page 767: 26

Answer

$$A = {33.72^ \circ },\,\,\,\,B = {38.94^ \circ },\,\,\,C = {107.34^ \circ }$$

Work Step by Step

$$\eqalign{ & a = 189{\text{yd,}}\,\,\,b = 214{\text{yd,}}\,\,\,c = 325{\text{yd}} \cr & \cr & {\text{Use the law of cosines to solve for any angle of the triangle}} \cr & {c^2} = {a^2} + {b^2} - 2ab\cos C \cr & {\text{Solve for cos }}C \cr & \cos C = \frac{{{a^2} + {b^2} - {c^2}}}{{2ab}} \cr & {\text{Substitute}} \cr & \cos C = \frac{{{{\left( {189} \right)}^2} + {{\left( {214} \right)}^2} - {{\left( {325} \right)}^2}}}{{2\left( {214} \right)\left( {214} \right)}} \cr & {\text{Use a calculator}} \cr & \cos C \approx - 0.298026999 \cr & {\text{Use the inverse cosine function}} \cr & C \approx {107.34^ \circ } \cr & \cr & {\text{Use the Law of sines to find the angle of }}B \cr & \frac{{\sin B}}{b} = \frac{{\sin C}}{c} \cr & \sin B = \frac{{b\sin C}}{c} \cr & \sin B = \frac{{214\sin \left( {{{107.34}^ \circ }} \right)}}{{325}} \cr & {\text{Use a calculator}} \cr & \sin B \approx 0.6285364106 \cr & {\text{Use the inverse sine function}} \cr & B \approx {38.94^ \circ } \cr & \cr & {\text{Calculate }}A \cr & A = {180^ \circ } - B - C \cr & A = {180^ \circ } - {38.94^ \circ } - {107.34^ \circ } \cr & A = {33.72^ \circ } \cr & \cr & {\text{Answer}} \cr & A = {33.72^ \circ },\,\,\,\,B = {38.94^ \circ },\,\,\,C = {107.34^ \circ } \cr} $$
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