An interactive applet and associated web page that demonstrate the concept of collinear points. Four draggable points are shown. Dragging any one of them will cause the others to move so they are always collinear. A button controls the line that can be drawn through them.

Applet can be enlarged to full screen size for use with a classroom projector. After use in the classroom, student can access it again from any web browser at home or in the library with no login required.

This resource is a component of the Math Open Reference Interactive Geometry textbook project at http://www.mathopenref.com.