(-2又3/5)+(+3又1/4)+(-3又2/5)+(+2又3/4)+(-1又1/2)+(-1又1/3)=(3又1/4+2又3/4)-(2又3/5+3又2/5)-1又1/2-1又1/3=6-6-1又3/6-1又2/6=-2又5/6
(-2又3/5)+(+3又1/4)+(-3又2/5)+(+2又3/4)+(-1又1/2)+(-1又1/3) = -2+3-3+2-1-1-3/5+1/4-2/5+3/4-1/2-1/3 =-2又5/6
-2又2/3