1. The problem statement, all variables and given/known data Let A be an idempotent matrix (A^2=A) a) show that I-A is also idempotent b) show that I+A is nonsingular and (I+A)^(-1)=I-(1/2)*A 2. Relevant equations 3. The attempt at a solution I managed to solve part a, but have a little problem solving b. I tried (I+A)*(I+A)^(-1)=(?)I but didn't know how to treat (I+A)^(-1) Thanks, Roni.