As you drag the ball along the perimeter of the circle, a line is drawn between the point on the circle and the corresponding point on the sine curve. The range is from 0 to 360 degrees on the circle and from 0 to 2 PI on the sine curve. For each point, lines are also drawn to represent the values of the sine function (shown in blue) and the cosine function (shown in red) at that point. By dragging the ball along the circle, you can clearly see that as the value of the sine function increases, the value of the cosine function decreases, and vice versa.
The lines were drawn with the Flash MX drawing API using the MovieClip methods MovieClip.moveTo(x, y) and MovieClip.lineTo(x, y). The circle, the ball, and the graph of the sine curve are all MovieClips.
This tool is based on Helen Triolo's exploration of the Flash 5 Math object. The two main differences are that this version is interactive and that it was written in Flash MX.