用简便方法计算下面各题.(1)199.199*198-198.198*199 (2)18.9*178.178+0.49-

(1)199.199*198-198.198*199
=199.199*（199-1）-198.198*199
=199（199.199-198.198）-199.199
=199.199-199.199
=0
(2)18.9*178.178-178.*189.189+0.49
=189*178（0.1*1.001-1.001）+0.49
=189*178（-0.9009）+0.49
=-30307.587