A epitrochoid is traced by a point attached to a circle of radius r rolling around the outside of a fixed circle of radius R, where the point is a distance d from the center of the interior circle. Use the sliders to adjust the radius R of the fixed circle, the radius r of the exterior circle, and the distance d of the point to the center of the interior of the circle.[br][br]Note the type of curve with different combinations of R, r, and d. When are there cusps and when is the curve smooth. The case where d=r is called an epicycloid and if R=r the curve is a limacon.[br][br]Move the slider to adjust the value of t to see the curve traced out - you can also click the play button in the lower left to animate.[br][br]To change the viewing window, hold the shift button and left-click to drag the graph or use the scroll wheel to zoom in/out. You can also adjust the axes by holding the shift button and left-click on the axis you want to change.