I need to plot the [Reuleaux triangle](https://en.wikipedia.org/wiki/Reuleaux_triangle) in rectangular coordinates.

[![Reuleaux triangle](https://i.stack.imgur.com/2lebl.png)](https://i.stack.imgur.com/2lebl.png)

I am not sure if there's a Reuleaux triangle equation. If yes, I can plot it by `ContourPlot`. 

I saw [link](http://mathworld.wolfram.com/ReuleauxTriangle.html) but I just need curve of Reuleaux triangle.

What's the best way to plot a Reuleaux triangle?