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Homework Help: Focus of parabola, checking my answer.

  1. Mar 4, 2012 #1
    I just had this question in an online test I took, and first I had 16ft, but for some unknown reason I chose to change it to 64ft right before I submitted the test, and of course I got it wrong. So I just want to confirm the answer is indeed 16ft.


    1. The problem statement, all variables and given/known data

    A parabolic antenna has a diameter of 32 feet and is 4 foot deep. How far is the focus from the vertex?


    2. Relevant equations



    3. The attempt at a solution

    attachment.php?attachmentid=44719&stc=1&d=1330896961.png

    My answer - Focus for this parabola is (0, a), so (0, 16) or 16ft from vertex
     

    Attached Files:

  2. jcsd
  3. Mar 4, 2012 #2

    LCKurtz

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    I think you have the depth and the diameter reversed.
     
  4. Mar 4, 2012 #3
    Hmm, not sure I understand why you think that.

    The way I read this is when x = 16, then y = 4, (the 'depth' 16 feet out to the bottom of the vertext is 4 feet), but maybe I misunderstood something.
     
  5. Mar 4, 2012 #4

    LCKurtz

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    Never mind. I had my two variables interchanged. You are correct.
     
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