How do you use the law of cosines or law of sines if you are given a=11, b=7, c=9?

1 Answer
Nghi N.
Jun 16, 2015

Solve triangle by Law of cosines and sines

Explanation:

To find a triangle's angle use the Law of Cosines

a^2 = b^2 + c^2 - 2bc.cos A
11^2 = 7^2 + 9^2 - 2(7)(9)cos A
cos A = (130 - 121)/126 = 9/126 = 0.07 --> A = 85.90
b^2 = a^2 + c^2 - 2ac.cos B
49 = 121 + 81 - 198cos B
cos B = 153/198 = 0.77 -> B = 39.40
Angle C = 180 - B - A = 180 - 39.40 - 85.90 = 54.70

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