解：??$(2)①0.\dot {7}=0.777···$??，??$0.\dot {7}×10=7.777···$??，
因?yàn)??$0.\dot {7}×10-0.\dot {7}=7$??，所以??$0.\dot {7}=\frac {7}{9} .$??
??$②0.\dot {2}\dot {3}=0.232323···$??，??$0.\dot {23}×100=23.232323···$??，
因?yàn)??$0.\dot {23}×100-0.\dot {23}=23$??，所以??$0.\dot {23}=\frac {23}{99} .$??
