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Forums->Cinderella Support (E)->Unable to construct a parabola by focus and directrix

hjbortol
3 stars
Unable to construct a parabola by focus and directrix


Hi!

In the Cinderella construction below, I'm unable to construct a parabola using the point "F" as focus and the line "k" as directrix:

http://www.professores.uff.br/hjbortol/tmp/unable-to-construct-parabola.cdy

When I activate the tool, Cinderella ask me to select focus and directrix. When I left click on the point F, Cinderella ask me to select a directrix. Then, when I left click on the line k, nothing happens and Cinderella ask me to select everything over again.

Note: the point F is computed using a CindyScript.

Thanks in advance, Humberto.
 
on: Sat 28 of Feb, 2009 [00:01 UTC] reads: 132497

Posted messages

author message
Re: Unable to construct a parabola by focus and directrix
on: Thu 12 of Mar, 2009 [05:03 UTC]
Dear Humberto,

yes, that seems to be a bug in displaying the parabola. Please send the file to bugs@cinderella.de and we will try to fix that!

Ulli

author message
DavidBakin
3 stars
Re: Unable to construct a parabola by focus and directrix
on: Mon 02 of Mar, 2009 [21:52 UTC]
Definitely a bug, but not in construction - perhaps in drawing.

If you look at the construction window you can see your parabola defined - twice! It is both C3 and C6. And as you move point g, thereby moving point F, you can see the equations for C3 and C6 change. But the parabola isn't drawn.

Neither is the parabola C2 - with G as focus as k as directrix - except for a certain range of point g - as you move g you can see C2 appear and disappear.

Finally, if you just define an arbitrary free point, and then define a parabola using it as focus and k as directrix, you can also see the parabola appear and disappear as you move the free point - sometimes. (For me it seems to depend on the position of point g - sometimes the parabola off the free point never disappears, but sometimes, e.g., when C2 is visible, it does sometimes disappear.

Very curious! — David



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