999*998998999-998*999999998=?注明解题思路
问题描述：
999*998998999-998*999999998=?注明解题思路
答
=999 x (998998998+1) - 998 x (999999999 -1)
=（999 x 998 x 1001001 +999）-（998 x 999 x1001001 -998)
=998 + 999
=1997