Algebra 2 (1st Edition)

Published by McDougal Littell
ISBN 10: 0618595414
ISBN 13: 978-0-61859-541-9

Chapter 13, Trigonometric Ratios and Functions - 13.6 Apply the Law of Cosines - 13.6 Exercises - Skill Practice - Page 892: 10

Answer

See below

Work Step by Step

We are given $A, b,c$. Use law of cosines to find $A$: $$a^2=b^2+c^2-2bc\cos A\\ \cos A=\frac{b^2+c^2-a^2}{2bc}\\A=\arccos \frac{b^2+c^2-a^2}{2bc}\\A=\arccos \frac{23^2+14^2-25^2}{2(23)(14)}\approx81.07^\circ$$ Use law of sines to find: $\frac{\sin B}{b}=\frac{\sin A}{a}\\\sin B=\frac{\sin A}{a}\times b\\\arcsin (\sin B)=\arcsin (\frac{\sin A}{a}b)\\B=\arcsin(\frac{\sin A}{a}. b)\\B=\arcsin(\frac{\sin 81.07^\circ}{25}. 23)\approx 65.35^\circ$ Since the sum of the triangle is $180^\circ$, we obtain: $$A+B+C=180^\circ\\C=180^\circ-A-B\\C=180^\circ -65.35^\circ - 81.07^\circ\\C\approx 33.58 ^\circ$$
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