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Results tagged with geometric-constructions
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user 4312
20
votes
How can we determine the center of a circle using a straightedge?
I do not think that it is possible.
Consider a projective map $f$ which preserves the circle; maps the center $O$ to a point $P\ne O$; and maps some point $Q$ to $O$. The line $QO$ is mapped to the li …
- 109k
22
votes
Accepted
Focus of parabola using only a ruler
No, because there exists a projective map which preserves the parabola but does not preserve its focus (this is so for any conic and any point.)
- 109k