2/(-3/7)*4/7/(-5又1/7): =2*(7/3)*4/7*(7/36)=14/3*1/9=14/27【15又1/2-(1又2/5+3又1/2】/(1又1/8)=[31/2-7/5-7/2]*8/9=(12-7/5)*8/9=53/5*8/9=424/451/5*(-5)/(-1/5)*5=-1/(-1)=1