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Homework Help: Polar equation

  1. Nov 15, 2006 #1
    I have the given polar equation that I have to graph.

    r = 5/(-1 + 2 cos θ)

    The format is r = ed/(1 +e cosθ)

    (e and d are always positive)

    I can solve multiply r by -1/-1 --> r = -5/(1 - 2 cosθ).

    Is this possible? I thought that the numerator (ed) cannot be a negative number. Is this a misprint or is there a way to solve this?
  2. jcsd
  3. Nov 15, 2006 #2
    r can be negative... it just means that you actually go 180 degrees the other direction. So for example, when theta is 180 degrees, r is -5/3... so the point is at 5/3 on the *positive* x-axis.
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