a = 2002 . 2002
= ( 2000 + 2 ) . 2002
= 2002 . 2000 + 2002 . 2
b = 2000 . 2004
= 2000 . ( 2002 + 2 )
= 2000 . 2002 + 2000 . 2
Ta thấy : 2000 . 2 = 2000 . 2 mà 2002 . 2 > 2000 . 2
\(\Rightarrow\) 2002 . 2000 + 2002 . 2 > 2000 . 2002 + 2000 . 2
\(\Rightarrow a>b\)
a = 2002.2004
a = (2000 + 2 ). 2002
a = 2000.2002 + 2.2002
b = 2000.2004
b = 2000.( 2002 + 2 )
b = 2000.2002 + 2000.2
Suy ra a>b