Atriangleis a geometric figure with three sides. Arectangleis a geometric
figure with four sides and four 90oangles. The opposite sides are equal in
length and are parallel. Asquareis a rectangle in which all sides are the same
length. A parallelogram has four sides with two pairs of parallel sides.
Atrapezoidhas four sides, two of which are parallel. Acircleis a geometric
figure such that all the points are the same distance from a point called its
center. The center is not part of the circle. A line segment passing through the
center of a circle and with its endpoints on the circle is called adiameter.
A line segment from the center of a circle to the circle is called aradius
(see Fig. 9-3).Perimeter
The distance around the outside of a geometric figure is called theperimeter
of the figure. The perimeter is found by adding the measures of all sides of the
geometric figure. For some geometric figures, there are special formulas that
are used to find their perimeters.166 CHAPTER 9 Informal Geometry
Fig. 9-2.Fig. 9-3.