4. WHAT IS A QUADRILATERAL?

Some definitions of figures may have to change in the Sketchpad environment. If you construct a quadrilateral with given sides abcd, the angles change and you can move the figure and investigate many properties of the set of figures. If you move the figure around, it sometimes crosses itself.

a. How do we want to describe this set of figures to include the crossed ones

b. Check out the area of the figure. How does Sketchpad calculate the area? Hint: Try adding the separate triangle areas.