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 \(c^2=a^2+b^2-2ab\cos(C)\)

Guest Jan 7, 2021

#1**+1 **

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

CoolStuffYT Jan 7, 2021