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Re: PolarPlot

dh wrote:
> Hi Bruce,
> the radius in polar coordinates has to be real and positive. Therefore, 

Actually, no. In polar coordinates r is a *directed* distance, which may 
be positive or negative.

> r=Sqrt[Cos[phi]] can not be the correct formula, we would get imaginary 
> values. To prevent this, we may e.g. write: r=Sqrt[Abs[Cos[phi]] what 
> gives the plot you are looking for.
> hope this helps, Daniel

Helen Read
University of Vermont

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