设斜率k则两条平行线方程：y=kx ==> kx-y=0y-3=k(x-1) ==> kx-y+(3-k)=0根号5=|3-k|/(k^2+1)^(1/2)5(k^2+1)=(3-k)^22k^2+3k-2=0(2k-1)(k+2)=0k=1/2或k=-2所以,两条平行线方程：y=(1/2)x 和y=(1/2)x+(5/2)或：y=-2x ...