Point E lies on segment AB, and point C lies on segment FG.
The area of parallelogram ABCD is 20 square units.
What’s the area of parallelogram EFGD?

Source: Alfred S. Posamentier, Math Wonders to Inspire Teachers and Students, 2003.)

Constructing in Geometer's Sketchpad, regardless of various reconfigurations, situations matching the given construction show the two parallelograms have the same area.

Posted by Charlie on 2017-08-01 10:11:30