y-1=k(x-2)y=kx+(1-2k)带入(3-k²)x²-2k(1-2k)x-(1-2k)²-3=0则x1+x2=2k(1-2k)/(3-k²)中点横坐标是(x1+x2)/2=k(1-2k)/(3-k²)=2k-2k²=6-2k²k=6所以是6x-y-11=0