1. The problem statement, all variables and given/known data If |A+B|^2=|A|^2+|B|^2, prove that A is perpendicular to B. 2. Relevant equations A^2=|A||A| 3. The attempt at a solution All I can think of to do is expand the equation to get (A.B)(A.B)=A.A+B.B. I know that iff a.b=0, the two are perpendicular but I can't figure out how to show that because I don't really even understand what the question is asking. I'm in desperate need of some help!