Choose one point p1 on line L, draw a circle c1, which intersects L at p2 and
centers at p1. Draw a circle c2 centered at P2. Then c1 and c2 intersect
p3,p4. Draw line L1 which passes O and p3 and intersects L at p5. Draw line L2
which passes O and P4 and intersects L at p6, Draw line L3 which passes p5 and
p4. Draw line L4 which passes p6 and p3. Then L4 and L3 intersect at p7. Draw
line L5 which passes p7 and O. Then L5 is what we want.
讲了答案就没劲了,我可以贴一个比较不错的结果,但是还有更好的结果:
O not on L: 2 circles
Choose one point p1 on line L, draw a circle c1, which intersects L at p2 and
centers at p1. Draw a circle c2 centered at P2. Then c1 and c2 intersect
p3,p4. Draw line L1 which passes O and p3 and intersects L at p5. Draw line L2
which passes O and P4 and intersects L at p6, Draw line L3 which passes p5 and
p4. Draw line L4 which passes p6 and p3. Then L4 and L3 intersect at p7. Draw
line L5 which passes p7 and O. Then L5 is what we want.
by yumyum
O on L: 3 circles
Draw a circle c1 centered at O, which intersects L at p2 and p3, draw
circles c2 and c3 centered at p2 and p3, which intersects c1 at p4p5(from c2)
and p6p7(from c3), assume p4p6 at the same side of the line L, draw line L2
which passes p2p4, draw line L3 which passes p3p6, L2 and L3 intersect at
point P7, connect P7 and O get the line we want.