It is proved that: (a + b-2ab) (a + b-2) + (1-ab) ^ 2 = (A-1) ^ 2 (B-1) ^ 2

It is proved that: (a + b-2ab) (a + b-2) + (1-ab) ^ 2 = (A-1) ^ 2 (B-1) ^ 2

Proof: (A-1) ^ 2 (B-1) ^ 2 - (1-ab) ^ 2 = [(A-1) (B-1) + (1-ab)] [(A-1) (B-1) - (1-ab)] = (ab-a-b + 1 + 1-ab) (ab-a-b + 1-1 + AB) = (- A-B + 2) (2ab-a-b) = (a + b-2ab) (a + b-2) (a + b-2ab) (a + b-2) + (1-ab) ^ 2 = (A-1) ^ 2 (B-1) ^ 2