1. The problem statement, all variables and given/known data Let D be an n x n diagonal matrix whose diagonal entries are either 0 or 1 a) Show that D is idempotent b) Show that if X is a nonsingular matrix and A=XD(X)-1 , then A is idempotent 2. Relevant equations 3. The attempt at a solution a) I tried it, and it works for a specific matrix, say 3x3... but I don't know if it's really a proof. I need to show that D2=D b) I solved this part Also, is (AB)2= A2*B2 or (AB)2=B2*A2 ?