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Circle as an implicit equation in polar form

The general polar equation of a circle of radius centered at is . This equation is derived from the Law of Cosines. Using that and we can transform this polar equation to a cartesian one:
Instead of the we use atan2(y,x) in GeoGebra, as this function gives us an angle in [0,360)
Another possibility is to use the general circle equation in cartesian form and substitute and so we get as the implicit equation.