Reflection About a Plane

In the applet below, the yellow triangular pyramid (with LARGE PINK VERTICES) has been reflected about the gray plane. You can alter the appearance of the yellow pyramid (pre-image) at any time by moving any one (or more) of the LARGE PINK VERTICES. You can change the orientation of the plane by moving any one (or more) of the 3 ORANGE POINTS it passes through. Explore! Be sure to answer the question that follows.


Suppose you stand 4 ft away from a mirror. How far would your image be away from the glass (assuming you could "reach in" and measure)? How is your conclusion somewhat supported by any dynamics you see here?

Quick (Silent) Demo