Transcript Polygons

POLYGONS
Poly = “MANY”
Gon = “ANGLES” OR “SIDES”
7th Grade Math
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.”
For our purposes, we will be
discussing only convex polygons, not
concave polygons.
REGULAR Polygon…
1. ALL sides congruent
2. ALL angles congruent
Example:
Square and Equilateral Triangle
What would it mean if I said, “I have
a regular pentagon”?
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. Remember,
polygons must have at least 3
sides.
3-sided polygon…
TRIANGLE.
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.
1. 100-meter hurdles
2. high jump
3. shot put
4. 200-meter dash
5. long jump
6. Javelin
7. 800-meter race on the second day.
Jackie Joyner-Kersee, an
American track-and-field
athlete, who won the
heptathlon event (an allaround 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
1994
1993
1992
1991
TEN YEARS
Sum of Interior Angles
Discuss the angle measures for:
Shape
# of sides
How many triangles in this
shape from one vertex?
Degrees in a triangle?
Degrees in Shape?
Triangle
3
1
180
180
Quadrilaterial
Pentagon
Hexagon
Heptagon
Octagon
Nonagon
Decagon
Can you create a formula that would work?
Formula to calculate the total
degrees in a polygon:
n = number of sides
(n-2)180
Scholastic “Sum of Interior
Angles” Activity
Practice:
Glencoe
Page 549
#1-5 #7-16