99..9(有n个9)*99...9(有n个9)+199...9(有n个9)
=(100..0(n个0) -1)*99...9(有n个9)+199...9(有n个9)
=99...900..0(有n个9,n个0)-99...9(有n个9)+199...9(有n个9)
=99...900..0(有n个9,n个0)+100..0(有n个0)
= 1 00.0(有2n个0)
99..9(有n个9)*99...9(有n个9)+199...9(有n个9)
=(100..0(n个0) -1)*99...9(有n个9)+199...9(有n个9)
=99...900..0(有n个9,n个0)-99...9(有n个9)+199...9(有n个9)
=99...900..0(有n个9,n个0)+100..0(有n个0)
= 1 00.0(有2n个0)