1. The problem statement, all variables and given/known data Let A and B be two square matrices of order n such that AB = A and BA = B. Then, what is the value of [(A + B)t]2? 2. Relevant equations 3. The attempt at a solution [(A + B)t]2 = AtAt + AtBt + BtAt + BtBt. I tried to use the fact that AB = A and BA = B to keep going but I didn't succeed at it..