Proof If A is an idempotent matrix (A2 = A), then prove
Chapter 3, Problem 3.3.83(choose chapter or problem)
Proof If A is an idempotent matrix (A2 = A), then prove that the determinant of A is either 0 or 1.
Unfortunately, we don't have that question answered yet. But you can get it answered in just 5 hours by Logging in or Becoming a subscriber.
Becoming a subscriber
Or look for another answer