# Folia of Descartes section plots

First of all, good day and thanks for taking the time to read this question. The problem I'm having, is how i can plot just sections of the Folia of Descartes graph, which is build from the equation:

$$x^3 + y^3 - 3xy=0$$

I'm trying to do the representations that Morris Tenenbaum and Harry Pollard do, in their Ordinary differential equation book, page 17.

So far i can do the plot of the Folia of Descartes using:

ContourPlot[x^3 + y^3 - 3 x y == 0, {x, -3, 3}, {y, -3, 3}, Axes -> True, Frame -> False]


And parametric plot:

ParametricPlot[{(3 m)/(1 + m^3), (3 m^2)/(1 + m^3)}, {m, -20, 80},PlotRange -> {-3, 3}]


Now i know that the option RegionFunction of the Function ParametricPlot could help for this, however i have failed in getting the sections.

I'm looking for any pointers or ideas on how to do the sections of the folia of descartes.

PS: My English isn't that good so I hope i explain my self good enough while making this question. Thanks again and have a good day.

As seen on Wikipedia, the folium of Descartes has a polar representation: $$r={\frac {3a\sin \theta \cos \theta }{\sin ^{3}\theta +\cos ^{3}\theta }}.$$

With this representation it's pretty easy to pick out relevant segments and to visualize them with PolarPlot.

f[min_, max_] := PolarPlot[
(3 Sin[t] Cos[t])/(Sin[t]^3 + Cos[t]^3), {t, min, max},
PlotRange -> 2.5, ImageSize -> 300,
PlotStyle -> Directive[Thickness[0.01], Black],
Epilog -> {HalfLine[{2^(2/3), 0}, {0, 1}], HalfLine[{0, 0}, {1, 1}]}
]

Row[{
f[0, Pi/4],
f[Pi/4 - 0.15, Pi/2]
}]


Row[{f[Pi/2, 2 Pi/3], f[5 Pi/6, Pi]}]


You can combine images with Show. You could also extend f to take several intervals of t.

• Awesome thanks, this helps a lot. Sep 9, 2016 at 19:18