S ECTION 1-4 P OLYGONS

A polygon is a closed figure in a plane, formed by connecting segments endpoint to endpoint with each segment intersecting exactly two others. Each line segment is called a side of the polygon. Each endpoint, where the sides meet, is called a vertex.

N AMES FOR P OLYGONS We name polygons based on the number of sides on the polygon.

To name a polygon, we name the vertices in order: Pentagon ABCDE Pentagon DCBAE

E XAMPLES OF N AMING P OLYGONS

A diagonal of a polygon is a line segment that connects two nonconsecutive vertices. Remember segment DE is a side of the polygon.

A polygon is convex if no diagonal is outside the polygon. A polygon is concave if at least one diagonal is outside the polygon.

Two polygons are congruent if and only if they are exactly the same size and shape. This means:

If quadrilateral CAMP is congruent to quadrilateral SITE, then their four pairs of corresponding angles and four pairs of corresponding sides are also congruent.

E XAMPLE Which polygon is congruent to ABCDE?

P ERIMETER The perimeter of a polygon is equal to the sum of the lengths of its sides. The perimeter of the quadrilateral is 37 cm.

S PECIAL P OLYGONS Equilateral Polygons

Equiangular Polygons

Regular Polygons