两条平行线L1、L2之间的距离为3,且分别过点（2,0）和（0,-3）,求它们的方程.

L1:y=k(x-2) y=kx-2k kx-y-2k=0
L2:y+3=kx y=kx-3
(0,-3)到L1的距离=| k*0-(-3)-2k|/(x^2+(-1)^2)^0.5=3
| k*0-(-3)-2k|/(k^2+(-1)^2)^0.5=3
|3-2k|/(k^2+1)^0.5=3
(3-2k)^2=9(k^2+1)
4k^2-12k^+9=9k^2+9
5k^2+12k=0
k=0 k=-12/5
L1:y=0 L2:y=-3
L1:y=-12/5(x-2) L2:y=-12/5x-3