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Homework Help: Sketch the graph of 4x^2 + 9y^2 = 144. Is this an ellipse?

  1. Jan 11, 2007 #1
    I'm going to sketch the graph of the eq. 4x^2 + 9y^2 = 144

    This is an ellipse with its center at the origo and major semiaxis 6 and minor semiaxis 4. But how do I find the foci?
     
  2. jcsd
  3. Jan 12, 2007 #2
    [tex]a^2=b^2+c^2[/tex]
    where c is the focal length.

    the equation comes directly from one definition of ellipse:
    the sum of distance between any point on the ellipse and the foci = 2a.
     
  4. Jan 12, 2007 #3
    Ah, makes sense. Thank you!
     
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