Hwk help please

[Seedler]

I'm in summer school doing conics right now, and here's the question from the parabola unit I can't get: (not enough info given?)

The Primary reflector of the Hubble Space Telescope is parabolic and has a diameter of 4.27 m and a depth of 0.75 m.

a) If a camera is recording pictures at the focus of the reflector, how far is the camera from the vertex, to the nearest hundredth of a metre?

b) Write an equation in standard form that models the parabolic reflector.

Any hint/suggestion/idea/solution is greatly appreciated.

[tesco]

This help any:
parabola.JPG
f26.gif

[Seedler]

This help any:
parabola.JPG
f26.gif

Yes, now that I know what h and k are, I still don't have enough info (x, y?) to find P, which is the focus.

The question doesn't specify the vertex, focus, or the directrix.

[tesco]

I think X and Y are any point you want on the parabola... (try the point i put in my drawing).

[lynx]

4p(y-k) = (x-h)^2

There's nothing to tell you where h and k are so you can put them wherever you want them to be. 0,0 would be useful though. That being the case you can write the equation as
4py = x^2

so p = x^2/4y

At the rim of the reflector, x is the radius = 2.135m, y is the depth = 0.75m

The answer is ...



















1.52m