An interactive applet and associated web page that demonstrate vertical angles. The applet shows two intersecting line segments that create two pairs of vertical angles. As you drag the endpoints of the line segments, the angles change and show that the vertical pairs are always congruent.

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.