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: 21

Answer

$$\,c = 6.46{\text{m, }}A = {53.1^ \circ },\,\,B = {81.3^ \circ }$$

Work Step by Step

$$\eqalign{ & C = {45.6^ \circ },\,\,\,b = 8.94{\text{m,}}\,\,\,a = 7.23{\text{m}} \cr & {\text{Use the Law of cosines to find }}c \cr & {c^2} = {a^2} + {b^2} - 2ab\cos C \cr & {\text{Substitute}} \cr & {c^2} = {\left( {7.23} \right)^2} + {\left( {8.94} \right)^2} - 2\left( {7.23} \right)\left( {8.94} \right)\cos \left( {{{45.6}^ \circ }} \right) \cr & {\text{Use a calculator}} \cr & {c^2} \approx 41.74934 \cr & {\text{Take square roots and choose the positive root}} \cr & c \approx 6.46{\text{m}} \cr & \cr & {\text{Calculate the angle }}A{\text{ using the law of sines}} \cr & \frac{a}{{\sin A}} = \frac{c}{{\sin C}} \cr & \sin A = \frac{{a\sin C}}{c} \cr & \sin A = \frac{{7.23\sin \left( {{{45.6}^ \circ }} \right)}}{{6.46}} \cr & \sin A \approx 0.799634 \cr & A \approx {\sin ^{ - 1}}\left( {0.799634} \right) \cr & A = {53.1^ \circ } \cr & \cr & {\text{Calculate }}B \cr & B = {180^ \circ } - A - C \cr & B = {180^ \circ } - {53.1^ \circ } - {45.6^ \circ } \cr & B = {81.3^ \circ } \cr & \cr & {\text{Answer}} \cr & \,c = 6.46{\text{m, }}A = {53.1^ \circ },\,\,B = {81.3^ \circ } \cr} $$
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