3.5 Polygons

A polygon:Formed by 3 or more segments (sides), no two sides with common endpoints are collinear

Each side intersects exactly 2 other sides, one at each end point

Endpoints are called a Vertex (vertices)

Naming Polygons

Name by vertices

Ex: polygon ABCDEFG

Name by sides

# of Sides Type

3 Triangle

4 Quadrilateral

5 Pentagon

6 Hexagon

7 Heptagon

8 Octagon

9 Nonagon

10 Decagon

12 Dodecagon

n n-gon

Convex or Concave?

“Concave”

Looks like it is “caving” in

“Convex”

The other kind (close to a circle)

Convex pentagon Concave

pentagon

Concave octagon

Convex heptagon

Special PolygonsEquilateral

All sides the sameEquiangular

All angles the sameRegular

All sides and angles the same

Regular none of the above Regular

Regular Not a polygonequiangluar

Diagonals:Connect two nonconsecutive verticesPolygon PQRST has two diagonals from Q, QT and QS

PQ

R

S

T

PQ

R

S

T