# law of cosines

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law of cosines

m<c=60, a=12,b=15 triangle

• law of cosines -

The law of cosines is:

a^2 = b^2 + c^2 - 2cosA
or
b^2 = a^2 + c^2 - 2cosB
or
c^2 = a^2 + b^2 - 2cosC

the lower case letters are sides, the capital letters are for angles. For this problem, you would do

c^2 = 12^2 + 15^2 - 2cos60

That gives you side c. After that, you should be able to use the law of sines to find the other two angles of the triangle.

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