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Period of a polar curve

  1. Apr 2, 2008 #1
    How does one know when the a polar curve repeats itself?

    I usually go from 0 to 2pi but that sometimes get me into trouble.

    For example:

    Question says find the horizontal and vertical tangents of this curve..

    [tex] r=3cos\theta [/tex]

    I was like well.. you have horizontal tangents when

    [tex] \theta = \pi/2, 3\pi/2, 5\pi/2, 7\pi/2 [/tex]

    vertical tangets when

    [tex] \theta = 0, \pi/2, \pi, 3\pi/2 [/tex]

    until I looked at the solution manual and they have only first half of these points.. then I realized that the curve repeats itself at pi, not 2pi. So yeah any tricks to see when it ends? Thanks!
  2. jcsd
  3. Apr 2, 2008 #2

    Gib Z

    User Avatar
    Homework Helper

    Well graphing it may help, or otherwise; at theta = pi, the line will be going in the negative direction, but cos (pi) is negative 1, so it will start going positive again, ie it starts again.
  4. Apr 2, 2008 #3
    Ok, thanks
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