Ta có :
A = 2002 x 2002 = ( 2000 + 2 ) x 2002 = 2000 x 2002 + 2002 x 2 = 2000 x 2002 + 4004
B = 2000 x 2004 = 2000 x ( 2002 + 2 ) = 2000 x 2002 + 2000 x 2 = 2000 x 2002 + 4000
Vì : 2000 x 2002 = 2000 x 2002 nhưng 4004 > 4000 nên A = 2002 x 2002 > B = 2000 x 2004