321321×123-123123×321
=321*1001*123-123*1001*321
=0
369×135135135-369369369×135
=369*135*1001001-369*1001001*135
=0
1995×1995-1994×1994
=1995*(1994+1)-1994*(1995-1)
=1995*1994+1995-1994*195+1994
=1995+1994
=3989
321321×123-123123×321
=321*1001*123-123*1001*321
=0
369×135135135-369369369×135
=369*135*1001001-369*1001001*135
=0
1995×1995-1994×1994
=1995*(1994+1)-1994*(1995-1)
=1995*1994+1995-1994*195+1994
=1995+1994
=3989