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Finding the major and minor axis of ellipse

  1. Feb 10, 2013 #1
    An ellipse is represented by [itex] \rho(t)^2=x^2(t) + y^2(t)[/itex] where [itex]\rho(t)[/itex] is the distance from origin to the ellipse at a given time.

    The way the article used to find the major and minor axis is the take the derivative [itex]\frac{d(\rho^2(t))}{d t}=0[/itex] to find the maximum and minimum.

    My question is why it use [itex]\frac{d(\rho^2(t))}{d t}=0[/itex], not [itex]\frac{d\rho(t)}{d t}=0[/itex]?
     
  2. jcsd
  3. Feb 10, 2013 #2

    D H

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    Because it's easier and yields the same answers so long as ρ is never 0.
     
  4. Feb 10, 2013 #3
    Thanks, so all it is, is to avoid dealing with the square root [itex] x^2 + y^2[/itex]?
     
  5. Feb 10, 2013 #4

    D H

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    That's all it is. Why bother with the added complexity?
     
  6. Feb 10, 2013 #5
    Thanks, I thought I missed something.
     
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