Locating a Product with Three Points and a Circle
DRAG FACTORS A and B ← or → from O with your mouse.
MOVE IMAGE > Hold Shift and move the diagram on the screen with your mouse.
ZOOM IMAGE > Hold Shift and zoom in and out with your mouse wheel.
ENTER FACTORS > You can also enter factors into the A and B input boxes.
Reset the Applet to the default ℯ × - π by clicking the icon top right.
NOTE: The circle disappears when both factors are the same because a unique circle cannot be drawn from two points only.
Goto http://tube.geogebra.org/student/m639417 for another fun applet showing multiplication on the reals via similar triangles.