2002 x 20012001 - 2001x20022002
=2002 x 2001 x10001-201 x 2002 x 10001
= 0
2002 x 20012001 - 2001x20022002
=2002 x 2001 x10001-201 x 2002 x 10001
= 0
2002*20012001-2001*20022002
=2002*2001*10001-2001*2002*10001
=(2002-2002)*(2001-2001)*(10001-10001)
=0