Poly = “MANY” Gon = “ANGLES” OR “SIDES” 7th Grade Math POLYGONS Poly = “MANY” Gon = “ANGLES” OR “SIDES” 7th Grade Math

POLYGONS. 1. Three (3) or more line segments 2. CLOSED figure 3 POLYGONS! 1. Three (3) or more line segments 2. CLOSED figure 3. Line segments DO NOT cross or intersect

Polygon Examples: Do these meet the above 3 criteria?

Is this shape a polygon? Why or why not?

This shape is NOT “closed.”

Why can’t a polygon have only 2 sides?

With only 2 sides, the shape could not be “closed.”

Is this shape a polygon? Does it meet the 3 criteria?

YES, this IS a polygon.

This shape is two-dimensional, “closed”, has 12 sides, and lines do not intersect.

However, this is a special type of polygon called “concave.”

It’s called “concave” because some of the sides are “caved in.” This is not an important concept. I just want to introduce this to them. We are only discussing basic polygons.

For our purposes, we will be discussing only convex polygons, not concave polygons.

REGULAR Polygon… 1. ALL sides congruent 2 REGULAR Polygon… 1. ALL sides congruent 2. ALL angles congruent Example: Square and Equilateral Triangle This is important. Stress “regular” polygons and their characteristics. Draw pictures with examples.

Let’s learn the names for the first eight polygons.

Polygons! Polygon Name Picture Definition Prefix & Memory Device

A one-sided polygon is called…?

Trick question. There is no such thing as a one-sided polygon Trick question!!! There is no such thing as a one-sided polygon. Remember, polygons must have at least 3 sides.

3-sided polygon… TRIANGLE.

You can remember the prefix “tri” by thinking of a tricycle You can remember the prefix “tri” by thinking of a tricycle. A tricycle has 3 wheels.                                 

4-sided polygon… QUADRILATERAL.

You can remember the prefix “quad” by thinking “times four.” Quadruple means x 4

5-sided polygon… PENTAGON

You can remember this name by thinking about the building in Washington, D.C.

6-sided polygon… HEXAGON

You can remember that a hexagon has six sides because the words hexagon and six both have the letter “x.”

The hexagon is the polygon of choice for bees.

7-sided polygon… HEPTAGON.

You can remember the prefix “hept” by thinking of the heptathalon in the Olympics. heptathlon—a two-day event in which athletes compete SEVEN DIFFERENT EVENTS. 100-meter hurdles high jump shot put 200-meter dash long jump Javelin 800-meter race on the second day.

Joyner-Kersee, Jackie Jackie Joyner-Kersee, an American track-and-field athlete, who won the heptathlon event (an all-around event) at the Olympic Games in 1988 and 1992. She is considered one of the greatest female athletes.

8-sided polygon… OCTAGON

You can remember the prefix “oct” by thinking of an octopus (that has 8 legs).

9-sided polygon… NONAGON

You can remember that a nonagon has nine sides because the words nonagon and nine both have two “ns.”

10-sided polygon… DECAGON

You can remember the prefix “dec” by thinking about a decade, which has 10 years. 2000 1999 1998 1997 1996 1995 TEN YEARS 1994 1993 1992 1991

How many triangles in this shape from one vertex? Sum of Interior Angles Discuss the angle measures for: Can you create a formula that would work? Shape # of sides How many triangles in this shape from one vertex? Degrees in a triangle? Degrees in Shape? Triangle 3 1 180 Quadrilaterial Pentagon Hexagon Heptagon Octagon Nonagon Decagon

Formula to calculate the total degrees in a polygon: n = number of sides (n-2)180

Scholastic “Sum of Interior Angles” Activity SUBSTITUTE: You do NOT have to do this activity.  Thanks!

Practice: Glencoe Page 549 #1-5 #7-16