1. 1-4 Vocabulary polygons concave/convex vertex side diagonal n-gon
regular polygon perimeter
area height

2. Each segment that forms a polygon is a side of the polygon
Each segment that forms a polygon is a side of the polygon. The common endpoint of two sides is a vertex of the polygon. A segment that connects any two nonconsecutive vertices is a diagonal.

3. You can name a polygon by the number of its sides
You can name a polygon by the number of its sides. The table shows the names of some common polygons.
A polygon is a closed plane figure formed by three or more segments that intersect only at their endpoints.
Remember!

4. Example 1: Identifying Polygons
Tell whether the figure is a polygon. If it is a polygon, name it by the number of sides.
polygon, hexagon
polygon, heptagon
not a polygon

5. All the sides are congruent in an equilateral polygon
All the sides are congruent in an equilateral polygon. All the angles are congruent in an equiangular polygon. A regular polygon is one that is both equilateral and equiangular. If a polygon is not regular, it is called irregular.
A polygon is concave if any part of a diagonal contains points in the exterior of the polygon. If no diagonal contains points in the exterior, then the polygon is convex. A regular polygon is always convex.

6. Example 2A: Classifying Polygons
irregular, convex
regular, convex
irregular, concave
regular, convex

7. The perimeter P of a plane figure is the sum of the side lengths of the figure.
The area A of a plane figure is the number of non-overlapping square units of a given size that exactly cover the figure.

9. The base b can be any side of a triangle
The base b can be any side of a triangle. The height h is a segment from a vertex that forms a right angle with a line containing the base. The height may be a side of the triangle or in the interior or the exterior of the triangle.

10. Perimeter is expressed in linear units, such as inches (in
Perimeter is expressed in linear units, such as inches (in.) or meters (m). Area is expressed in square units, such as square centimeters (cm2).
Remember!

11. Lesson Quiz: Part I
Find the area and perimeter of each figure. 3.

12. Find the area of triangle ABC with A(-2,4), B(6,4) and C(0,8)
Lesson Quiz: Part II
1. Find the perimeter of polygon LMNP with coordinates L(1, 4) M(4, 0) N(2, 0)
P(-1, -2)
Find the area of triangle ABC with
A(-2,4), B(6,4) and C(0,8)