√(1......1-2......2)
=√(1......10......0-1......1)____拆项
=√[1......1•(10......0-1)]___________提取公因式
=√(1......1•9......9)
=√(1......1²•9)________________________开方
=1......1•3
=3......3
也就是说,里头有n个1,结果就是n-1个3
√1……（n个1）-2……（n个2）=
……（n个3）