负三分之二加上负六分之一减去负负四分之一减去二分之一=(-2/3)+(-1/6)-[-(-1/4)]-1/2=-2/3-1/6-1/4-1/2=-(2/3+1/6+1/4+1/2)=-(4/6+1/6+1/4+2/4)=-(5/6+3/4)=-(10/12+9/12)=-19/12
