Chapter Three:  
Parallel and Perpendicular Lines

Geometry   Notes

Chapter  3

Section  3.1
Section  3.2
Section  3.3
Section  3.4
Section  3.5
Section  3.6
Section  3.7

Geometry Contents

Take notes on the following topics.

Section 3-4  The Polygon Angle-Sum Theorem

Vocabulary

Polygon (p. 143) A polygon is a closed plane figure with at least three sides that are segments. The sides intersect only at their endpoints and no two adjacent sides are collinear. The vertices of the polygon are the endpoints of the sides. A diagonal is a segment that connects two nonconsecutive vertices. 

Convex polygon (p. 143) A polygon is convex if no diagonal contains points outside the polygon.

Concave polygon (p. 143) A polygon is concave if a diagonal contains points outside the polygon.

Equilateral  polygon (p.146) An equilateral polygon is a polygon whose sides are all congruent.

Equiangular  polygon (p. 133) An equiangular polygon is a polygon whose angles are all congruent.

Regular polygon (p. 146) A regular polygon is a polygon that is both equilateral and equiangular. Its center is the center of the circumscribed circle.

 

Theorem 3-9  Polygon Angle-Sum Theorem

The sum of the measures of the angles of an n-gon is (n – 2)180

Theorem 3-10  Polygon Exterior Angle-Sum Theorem

The sum of the measures of the exterior angles of a polygon, one at each vertex, is 360.