a=-1/2 b=-1/2 c=-3/4过程把①代入②a/2-b-(a+b/2)=1 得到a=-2-3b把a=-2-3b代入③3×（-2-3b）+b=-2 得到b=-1/2把b=-1/2代入③3 a+（-1/2）=-2得到a=-1/2把a=-1/2，b=-1/2代入①-1/2+（-1/2）÷2=c=-3/4