Michael J. answered 05/18/15
Tutor
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Effective High School STEM Tutor & CUNY Math Peer Leader
Use law of cosine.
c2 = a2 + b2 - 2abCosC
where:
a, b, c are side lengths. C is the angle opposite of side c.
Given:
a = 550
b = 585
c = 145
Plug in the values into the formula for law of cosine.