Page 223 - ABCTE Study Guide_Neat

Notice that each quadrilateral can be cut into two triangles. Since the sum of the measures of the angles
in a triangle is 180°, and each quadrilateral is composed of two triangles, then the sum of the measures of
the angles in a quadrilateral is twice the sum of the measures of the angles in a triangle: 2 x 180° = 360°.

The sum of the measures of the angles in a quadrilateral is 360°.

Review

• A polygon is a closed figure made of segments called sides.
• A triangle is the simplest polygon. It has three sides.
• Triangles may be classified by their sides or by the measures of their angles.

Properties of Polygons

Lesson Objective

In this lesson, we'll explore a few properties of polygons.

Previously Covered

In the previous lesson we looked at examples of triangles and quadrilaterals.

Polygon literally means "many knees," but mathematicians use it to mean "many sides." In the table
below you will find the names of the most common polygons. See if you can find a relationship between
the number of angles a polygon has and the number of sides it has. This relationship will explain why
polygons have come to be classified by the number of sides they have, rather than the number of angles
they have. While you’re at it, see if you can find a relationship between the numbers of sides, angles, and
vertices.