2(x-y)/3-(x+y)/4=-13(x+y)-6(x-y)=6一式去分母得 8(x-y)-3(x+y)=-12二式除3得 (x+y)-2(x-y)=2设x+y为a,x-y为b代入原式8b-3a=-1①a-2b=2a=2b+2　②②代入①得 8b-3(2b+2)=-128b-6b-6=-122b=-12+62b=-6b=-3 ③③代入...