∵L1//L2
∴3/a=(a-2)/1
得3=a²-2a
a²-2a-3=0
(a-3)(a+1)=0
a=3舍去
a=-1
L2:-3x+3y-2=0
x-y+2/3=0
L1：x-y+6=0
d=|2/3-6|√2=8√2/3
两直线之间的距离为8√2/3