211: Wait a Minute, Square.

Take a moment to check that each piece in the top diagram is identical to its counterpart in the bottom one.

If you want to recreate this in Geogebra ...

1. turn on grid.
2. insert the polygons in this order: green triangle, black rectangle, yellow L-shape.
3. insert a segment up the "middle" at the appropriate x-position.
4. locate the intersection point of the segment and the hypotenuse of the triangle.
5. insert the two final polygons.
6. Click on each polygon, and copy-paste and build the second figure below the first one.