A is square, A^2 = A ----> det(A) = 0 or 1 1. The problem statement, all variables and given/known data I need to prove the thread title. 2. Relevant equations The only relevant equation I can think of is det(A) = 0 <---> A * inv(A) = I 3. The attempt at a solution Been toying around with it but not getting anywhere. Help, brahs?