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Just a quick question- when is the Law of Cosines \(c^2=a^2+b^2+2ab\cos(C)?\) I thought it was if the triangle you were using the Law of Cosines on was obtuse, but I'm confused because when I browse on the internet it says it always is \(c^2=a^2+b^2-2ab\cos(C)\)

 Jan 7, 2021
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It is always with -2ab*cos(C). When C is obtuse, then cos(C) is negative and so -2ab*cos(C) is positive.

 

You are very welcome!

:P

 Jan 7, 2021

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