- #1

- 3

- 1

So I read a description saying something along the lines of, a Parabola does have a 2nd focus and directrix, but that they stretch off into infinity, whereas for the hyperbola the 2nd focus comes back round..?

Anyway, I'm trying to picture it and understand in relation to the eccentricity,

I get the feeling I'm missing something obvious..

Cheers!

Edit:

So I think I need to clarify my question a bit. My understanding is that a circle, ellipse, parabola and hyperbola are all specific cases of the same formula. The ratio between the the radius and the distance to the 'directrix' is called the eccentricity. When

Anyway, I'm trying to picture it and understand in relation to the eccentricity,

*e.*What is it about*e=1*(value for a parabola), that determines there is only one focus, directrix and curve as opposed to a hyperbola,*e>1*, that means there are two foci, directrices and curves.?I get the feeling I'm missing something obvious..

Cheers!

Edit:

So I think I need to clarify my question a bit. My understanding is that a circle, ellipse, parabola and hyperbola are all specific cases of the same formula. The ratio between the the radius and the distance to the 'directrix' is called the eccentricity. When

*e*=1, we have a parabola. When*e>1*then we have a hyperbola. What I don't understand is, what happens when*e>1*to lend the hyperbola the property of having two foci and two directrices, when at*e=1*we had a parabola with only 1 focus and 1 directrix.
Last edited: