设l1:ax+by+c=0l2:ax+by+d=0l1经过原点 => c=0l2经过点(1,3) =>a+3b+d=0距离为根号5 => d^2/(a^2+b^2)=5以上3式得出:(1)b=a/2,d^2=25a^2/4 l1:x+y/2=0l2:x+y/2-5/2=0(2)b=-2a,d^2=25a^2 l1:x-2y=0 l2:...