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August 21, 2014

Homework Help: Trig. Law of Cosines

Posted by ashley on Tuesday, December 12, 2006 at 5:45pm.

Show that any triangle with standard labeling...
a^2+b^2+c^2/2abc = cos(alpha)/a + cos(beta)/b + cos(gamma)/c



I don't get it. Can someone please help me.



Start here with the law of cosines:
a^2 = b^2 + c^2 -2bc Cos A
b^2 = a^2 + c^2 -2ac Cos B
c^2 = a^2 + b^2 - 2ab Cos C

Add the three equations. divide both sides by 2abc

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