SOLUTION: find angle A of the oblique triangle with sides a=13, b=14, and c=15

Question 150945: find angle A of the oblique triangle with sides a=13, b=14, and c=15
Answer by mducky2(62) (Show Source): You can put this solution on YOUR website!
If you need to find an angle when three sides of an oblique triangle are known, use the law of cosines. The equation is:
a² = b² + c² - 2bc cos A

Solve for A
2bc cos A = b² + c² - a²
cos A = (b² + c² - a²)/(2bc)
A = cos^-1[(b² + c² - a²)/(2bc)]
A = cos^-1[(14² + 15² - 13²)/(2*14*15)]
A = 53.13°
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