SOLUTION: A=9 C=5 B=120 degrees find the measure of angle A

Question 1030011: A=9 C=5 B=120 degrees find the measure of angle A
Answer by stanbon(75887) (Show Source): You can put this solution on YOUR website!
A=9 C=5 B=120 degrees find the measure of angle A
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Draw a 120 degree angle; Let the sides be A = 9 and C = 5
Find side B using Law of Cosines::
B^2 = A^2 + C^2- 2A*C*cos(120)
B^2 = 81 + 25 - 2*9*5*(-1/2)
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B^2 = 151
B = 12.29
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Find angle A using Law of Cosines::
cos(A) = [B^2+C^2-A^2]/(2B*C)
cos(A) = [151+25-81]/(2*12.29*5) = 0.7730
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angle A = arcCos(0.7730) = 39.38 degrees
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Cheers,
Stan H.
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