Ta có :
* 2002 x 2002
= ( 2000 + 2 ) x 2002
= 2000 x 2002 + 2 x 2002
* 2000 x 2004
= 2000 x ( 2002 + 2 )
= 2000 x 2002 + 2 x 2000
Vì 2000 x 2002 = 2000 x 2002 ; 2 x 2002 > 2 x 2000
=> 2000 x 2002 + 2 x 2002 > 2000 x 2002 + 2 x 2000
Hay 2002 x 2002 > 2000 x 2004
Vậy 2002 x 2002 > 2000 x 2004