Let a and B belong to R. compare the relationship between a square + b square + 1 and ab + A + B

Let a and B belong to R. compare the relationship between a square + b square + 1 and ab + A + B

2(a²+b²+1)-2(ab+a+b)
=2a²+2b²+2-2ab-2a-2b
=(a²-2ab+b²)+(a²-2a+1)+(b²-2b+1)
=(a-b)²+(a-1)²+(b-1)²
≥0
SO 2 (A & sup2; + B & sup2; + 1) ≥ 2 (AB + A + b)
A & sup2; + B & sup2; + 1 ≥ AB + A + B (take the equal sign when a = b = 1)