**Warm-Up**

Warm-Up for Polygons introduction

**Polygons**

Plane figure (2-D) made up of straight sides (line segments, not curved) that are all connected (closed, not open)

Examples and Non-Examples given in class:

**Concave**

(informal definition)- Polygon with an “indent” in it

(Formal definition)- Polygon with at least 1 interior angle measure of greater than 180º

**Convex**

(informal defintion)- Polygon that is not concave

(Formal definition)- Polygon whose interior angles all have measures less than 180º

**Regular Polygon-** polygon whose angles are all congruent, and sides are all congruent.

**Naming Polygons**

Named by their number of sides:

3- Triangle

4- Quadrilateral

5- Pentagon

6- Hexagon

7- Septagon/Heptagon

8- Octagon

9- Nonagon

10- Decagon

11- Hendecagon

12- Dodecagon