In the right panel is a picture of a rectangle with a given height and width and therefore
a well-defined Area and Perimeter.
In the left panel is a graph of height vs. width, with a RED dot at a position that
corresponds to the height and width of the rectangle in the right panel.
You can change the rectangle by dragging the RED dot.
You can leave a mark at the current position by clicking the "mark this point" button.
[you may need graph paper to answer the following questions]
along what curve in the height-width plane are all the
▪ squares?
▪ similar rectangles?
▪ rectangles of a given perimeter?
▪ rectangles of a given area?
▪ rectangles whose diagonal has a given value?
Make up another question to ask.