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Thread: Hwk help please

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    Seedler's Avatar T__________________T
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    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.
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    tesco's Avatar woowoo
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    This help any:
    parabola.JPG
    f26.gif

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    Seedler's Avatar T__________________T
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    Quote Originally Posted by rossco
    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.
    Last edited by Seedler; 07-22-2006 at 04:25 AM.
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    tesco's Avatar woowoo
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    I think X and Y are any point you want on the parabola... (try the point i put in my drawing).

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    lynx's Avatar .
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    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
    .
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