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# FP3 Loci Question watch

1. Q. 8 b) The directrix is +- 4/root3, so why does the mod of PF1 and the mod of PF2 not equal 8roo3, considering that the distance of an arbitrary point on the ellipse x, from the focus is the same as that from the directrix?
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2. Please do not reply to this thread, I realise that the above definition only applies to a parabola.
3. (Original post by Prajna)
Q. 8 b) The directrix is +- 4/root3, so why does the mod of PF1 and the mod of PF2 not equal 8roo3, considering that the distance of an arbitrary point on the ellipse x, from the focus is the same as that from the directrix?
I wrote the solution to this paper in a thread last June
I will look to find it
4. (Original post by TeeEm)
I wrote the solution to this paper in a thread last June
I will look to find it
Thanks, but it doesn't matter, I realise my mistake.
5. (Original post by Prajna)
Q. 8 b) The directrix is +- 4/root3, so why does the mod of PF1 and the mod of PF2 not equal 8roo3, considering that the distance of an arbitrary point on the ellipse x, from the focus is the same as that from the directrix?
I offer no help, but did you know that, for a > b and where P is any general point and S and S' are foci, you can probe that for any case? Try it out!

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