Let be the three sides of a triangle , and let
, be the angles opposite them. If ,
Huh.. that was long..
First thing I thought about this equation was the law of cosines. We'll use it later as expected.
Let's start of with reducing this.
Law of sines tell us that
From here we get and .
By using them,
It's simple enough now. Time to find by the law of cosines..
By the law,
We got now. By using it,