http://www.ck12.org Chapter 1. Basics of Geometry
1.6 Classifying Polygons
Learning Objectives
- Define triangle and polygon.
- Classify triangles by their sides and angles.
- Understand the difference between convex and concave polygons.
- Classify polygons by number of sides.
Review Queue
- Draw a triangle.
- Where have you seen 4, 5, 6 or 8-sided polygons in real life? List 3 examples.
- Fill in the blank.
a. Vertical angles are always __.
b. Linear pairs are __.
c. The parts of an angle are called ____ and a ____.
Know What?The pentagon in Washington DC is a pentagon with congruent sides and angles. There is a smaller
pentagon inside of the building that houses an outdoor courtyard. Looking at the picture, the building is divided up
into 10 smaller sections. What are the shapes of these sections? Are any of these division lines diagonals? How do
you know?
Triangles
The first enclosed shape to examine is the triangle.
Triangle:Any closed figure made by three line segments intersecting at their endpoints.
Every triangle has threevertices(the points where the segments meet), threesides(the segments), and threeinterior
angles(formed at each vertex). All of the following shapes are triangles.