Reuleaux Triangle

這個好玩...鑽孔鑽出正方形

參考資料：
http://mathworld.wolfram.com/ReuleauxTriangle.html
http://whistleralley.com/ellipse/ellipse.htm
http://kmoddl.library.cornell.edu/tutorials/02/
http://whistleralley.com/reuleaux/reuleaux.htm
http://en.wikipedia.org/wiki/Curve_of_constant_width