A square matrix A is called idempotent if A> = A. (The word idempotent comes from the Latin idem, meaning \"same,\" and potere, meaning \"to have power.\" Thus, something that is idempotent has the \"same power\" when squared.) a. Find three idempotent 2 x 2 matrices. b. Prove that the only invertible idempotent x n matrix is the identity matrix