I have a problem with this question where I need to show the law of cosines (c^2=a^2+b^2-2ab*cos(angle) is an immediate consequence of the identity: (a+b)^2=a^2+b^2+2ab. I've played around with it for awhile and come somewhat close but can't get quite all the way there. It's basically all an algebraic problem but I'm not too good at that when deriving other equations. I drew a triangle with sides a,b, and c, to try to re-write the 2ab part as 2(c*cos(angle))^2 but don't know how to get rid of one to have 2abCos(angle). Any bit of help or just a hint could probably get me through this.(adsbygoogle = window.adsbygoogle || []).push({});

**Physics Forums | Science Articles, Homework Help, Discussion**

Join Physics Forums Today!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

# Homework Help: Law of cosines being an immediate consequence of

**Physics Forums | Science Articles, Homework Help, Discussion**