1)
999*999+1999＝1000*999-999+1999=1000000
2)
2005*20062006-2006*20052005
=2006*20062006-2006*20052005-20062006
=2006(20062006-20052005)-20062006
=2006*1001-20062006
=20062006-20062006
=0