16-19. Demonstrate that 0 R2 1. (Hint: Use ni =1 xiyi = 1x2 i...

16-19. Demonstrate that 0 ≤ R2 ≤ 1. (Hint: Use ni

=1 xiyi = ˆ β1x2 i to verify thatni

=1 y2i

≥ ni

=1 e2 i

≥ 0.)