Timeline for Focus of parabola using only a ruler
Current License: CC BY-SA 3.0
7 events
| when toggle format | what | by | license | comment | |
|---|---|---|---|---|---|
| Apr 28, 2016 at 8:35 | comment | added | Fedor Petrov | Assume that there is some construction on the plane $\pi$ which given parabola $\gamma$ gives its focus $F$. Let $T$ be projective map for which $T(\gamma)$ is a parabola again, but $T(F)$ is not it's focus. Apply the same construction to $T(\gamma)$ on $T(\pi)$, we get $T(F)$. Contradiction. | |
| Apr 28, 2016 at 7:39 | comment | added | Ivan Meir | You need to define the focus and by doing so I guess you might already see that this is not projective. Also there are points that are always preserved by a projective transform, the point at infinity in the case of the parabola so this contradicts your final statement. Can you modify it to make it always hold? | |
| Apr 28, 2016 at 7:32 | comment | added | Ivan Meir | How do you prove this? | |
| Jan 1, 2015 at 20:02 | history | edited | Fedor Petrov | CC BY-SA 3.0 |
added 1 character in body
|
| Dec 31, 2014 at 17:38 | vote | accept | Victor | ||
| Dec 31, 2014 at 17:38 | comment | added | Victor | Fantastic! It's very easy and hence beautiful and hence genius! Happy New Year | |
| Dec 31, 2014 at 16:48 | history | answered | Fedor Petrov | CC BY-SA 3.0 |