The four green points are the vertices of a quadrilateral.[br]The orange, blue and yellow points can be moved, changing the shape of the quadrilateral.[br]The quadrilateral usually contains a circle touching all four of its sides.[br]Explore and take note of your observations ...[br]Source: [url=https://pdst.ie/sites/default/files/S%26S%20manual_22.11.13.pdf]https://pdst.ie/sites/default/files/S%26S%20manual_22.11.13.pdf[/url], page 157.