Using sliders to change the radius of a circle.

This program uses the trigonometric functions sine and cosine to draw a circle.
Why, you might ask, use trig, when there is a built-in Javascript function for drawing circles?
Well, it is because by drawing a circle point-by-point, be can change the radius while the circle is being drawn!
From 11th grade math, you know the equation of a circle, in as a function of the radius and angle is:

r (radius):