差=-1-(-5/12-7/8-3/4)=-1-(-10/24-21/24-18/24)=-1-(-49/24)=-1+49/24=25/24
(-1)- [ (-5/12)+(-7/8)+(-3/4)]=(-1)-[(-10/24)+(-21/24)+(-18/24)]=(-1)-(-49/24)=(-1)+(49/24)=25/24
