The geometric objects we have studied until now have been relatively simple: just lines, triangles, and circles. In the remainder of the book we will need to use polygons with more sides; specifically, we will study four-sided and six-sided figures. This chapter contains the necessary information about four-sided polygons.

Let us begin by repeating the definitions from Chapter 0. Four points*A , B , C ,*and*D*such that no three are collinear determine a*quadrilateral*denoted by

The four segments are the*sides*of the