Wolfram Demonstrations Projecthttp://demonstrations.wolfram.com/An Open Resource of Interactive Mathematica VisualizationsCopyright 2009 Wolfram Demonstrations Project & ContributorsDrawing Some Plane Curves Using Envelopes of Lineshttp://demonstrations.wolfram.com/DrawingSomePlaneCurvesUsingEnvelopesOfLines/]]>http://demonstrations.wolfram.com/DrawingSomePlaneCurvesUsingEnvelopesOfLines/