Trigonometry 7th Edition

Published by Cengage Learning
ISBN 10: 1111826854
ISBN 13: 978-1-11182-685-7

Chapter 7 - Section 7.2 - The Law of Cosines - 7.2 Problem Set - Page 378: 14

Answer

$C \gt B \gt A$. Therefore the largest angle is $\angle C = 68.7˚$.

Work Step by Step

1. Use the cosine formula to find $\angle C$ $c^{2} = a^{2} + b^{2} - 2abcos(C)$ $(26)^{2} = (22)^{2} + (24)^{2} - 2(22)(24)cos(C)$ $676 = 1060 - 1056cos(C)$ $-384 = -1056cos(C)$ $0.363636... = cos(C)$ by GDC / calculator $C = 68.6763...˚$ $C = 68.7˚$ 2. Use the sine formula to find $\angle A$ and $\angle B$ $\frac{sin(A)}{22}= \frac{sin(68.6763...)}{26}$ $sin(A) = \frac{22sin(68.67...)}{26}$ by GDC / calculator $sin(A) = 0.78822...$ $A = 52.0201...˚$ $A = 52.0˚$ $\frac{sin(B)}{24} = \frac{sin(68.6763...)}{26}$ $sin(B) = \frac{24sin(68.6763...)}{26}$ $sin(B) = 0.85988....$ by GDC / calculator $B = 59.3035...˚$ $B = 59.3˚$ $C \gt B \gt A$. Therefore the largest angle is $\angle C = 68.7˚$.
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