1又1/2x5/7-(-5/7)x2又1/2+(-1/2)÷1又2/5=1又1/2x5/7+5/7x2又1/2-1/2x5/7=(1又1/2+2又1/2-1/2)x5/7=3又1/2x5/7=7/2x5/7=5/2