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## Recognize this plane curve?

An aspect of my work led to a plane curve with implicit equation $$x^2+y^2 = 3 (y/2)^{2/3} + 1$$ Actually, I started with the parametrization below and derived from it the equation above: \begin{eqnarray} x(t) &=& t (3-2 t^2) \\ y(t) &=& 2(1-t^2)^{3/2} \end{eqnarray}

Here is what it looks like:

If this falls in some classical class of curves, and perhaps even has a name, I would like to reference it appropriately. Does anyone recognize this curve? Thanks!

Answered. By Sylvain Bonnot and Francesco Polizzi: It is a type of nephroid! Here's the Wikipedia image from the article they both cited:

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 It is almost a nephroid (en.wikipedia.org/wiki/Nephroid ), except I can't exactly make the reparametrization right now. – Jan Jitse Venselaar May 31 2012 at 13:28

Your curve is a nephroid, see http://en.wikipedia.org/wiki/Nephroid.

The general equation of such a plane curve is $$(x^2+y^2-4a^2)^3=108a^4y^2.$$ Your example corresponds to the value $a=\frac{1}{2}$ of the parameter.

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 Thanks, Francesco! – Joseph O'Rourke May 31 2012 at 13:31

Pretty curve...I think it is a Nephroid: http://en.wikipedia.org/wiki/Nephroid

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 Thanks, Sylvain! – Joseph O'Rourke May 31 2012 at 13:31