This interactive diagram shows a red circle and within it drawn a blue
equilateral triangle. There are also a red dot to the right of the
circle and two yellow dots on the top left. You may drag the yellow
dots about and they will stay where 'dropped', but nothing else
changes. The point marked O at the middle is a fixed origin for the
diagram.

The red dot can be dragged to the right and left, with consequent
changes in the size of the circle and the triangle. Note that if you
drag the dot right out of the window the circle size will keep on
changing until you let go of the point; but if you drop the point
while it cannot be seen, you will have to refresh the window, thus
resetting the applet, and start again.

The red point labelled s0 can be dragged around the circle; the
triangle through labeled s0, s1 and s2, will rotate with it.

Clicking on the little square containing a question mark at the
diagram's bottom right will take you to the Geometer's Sketchpad Home
Page, if internet access is set up right.