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.