How to prove a (a-b) ≥ B (a-b) for real numbers a and B

How to prove a (a-b) ≥ B (a-b) for real numbers a and B

a(a-b)≥b(a-b)
∴a(a-b)-b(a-b)=(a-b)²≥0
∴a(a-b)≥b(a-b)