l2:dx+ey+f=0
y=(-d/e)x-(f/e)
l3:y=ex/d
ax-by+c=0
ax-bex/d+c=0
x=c/(be/d-a)=cd/(be-ad)
y=ce/(be-ad)
l3和l1交点M[cd/(be-ad) ,ce/(be-ad)]
y=ex/d
dx+ey+f=0
dx+e^2x/d+f=0
x=-f/(e^2/d+d)=-fd/(e^2+d^2)
y=-fe/(e^2+d^2)
l3和l2交点N[ -fd/(e^2+d^2),-fe/(e^2+d^2)]
设l3和对称直线l1'交于O
(Ox+Mx)/2=Nx,(Oy+My)/2=Ny
Ox=2Nx-Mx=-2fd/(e^2+d^2)-cd/(be-ad)
Oy=2Ny-My=-2fe/(e^2+d^2)-ce/(be-ad)
l1和l2交于P
ax-by+c=0
dx+ey+f=0
Px= -(ce+bf)/(ae+bd)
Py=(cd-af)/(bd+ae)
对称直线方程：y-Py=[(Py-Oy)/(Px-Ox) ] (x-Px)