Precalculus: Mathematics for Calculus, 7th Edition

Published by Brooks Cole
ISBN 10: 1305071751
ISBN 13: 978-1-30507-175-9

Chapter 6 - Section 6.5 - The Law of Sines - 6.5 Exercises - Page 514: 27

Answer

$a=26$ $;$ $b\approx30.871$ $;$ $c=15$ $\angle A\approx57.176^{\circ}$ $;$ $\angle B\approx93.824^{\circ}$ $;$ $\angle C=29^{\circ}$

Work Step by Step

$a=26$ $,$ $c=15$ $,$ $\angle C=29^{\circ}$ The Law of Sines is $\dfrac{\sin A}{a}=\dfrac{\sin B}{b}=\dfrac{\sin C}{c}$ Find angle $A$ using the formula $\dfrac{\sin A}{a}=\dfrac{\sin C}{c}$, obtained from the Law of Sines. Substitute the known values and solve for $A$: $\dfrac{\sin A}{26}=\dfrac{\sin29^{\circ}}{15}$ $\sin A=\Big(\dfrac{26}{15}\Big)\sin29^{\circ}$ $A=\sin^{-1}\Big[\Big(\dfrac{26}{15}\Big)\sin29^{\circ}\Big]\approx57.176^{\circ}$ Two angles are now known. Since $\angle A+\angle B+\angle C=180^{\circ}$, substitute the known angles into the formula and solve for $\angle B$: $B=180^{\circ}-29^{\circ}-57.176^{\circ}\approx93.824^{\circ}$ Find the side $b$ by using the formula $\dfrac{\sin B}{b}=\dfrac{\sin C}{c}$, obtained from the Law of Sines. Substitute the known values and solve for $b$: $\dfrac{\sin93.824^{\circ}}{b}=\dfrac{\sin29^{\circ}}{15}$ $\dfrac{b}{\sin93.824^{\circ}}=\dfrac{15}{\sin29^{\circ}}$ $b=\Big(\dfrac{\sin93.824^{\circ}}{\sin29^{\circ}}\Big)15\approx30.871$
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