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Geometry Notes
Section 1-6
What you’ll learn. . .
How to identify and name polygons
 Find perimeters of polygons

Vocabulary
Polygon
 Concave
 Convex
 n-gon
 Regular polygon
 perimeter

Polygons

Examples

Non examples:
DEFN: POLYGON

To name a
 a closed figure in a plane
polygon, list
 formed by connecting line segments
endpoint
consecutive
Consecutive
to endpoint (these line segments only
sides
intersect the other line segments vertices
at the
A polygon is
endpoints)

E
Parts of Polygons
 Each linePsegment is a called a SIDE
N
 Each
endpt where sides meet is a VERTEX
Diagonal
Consecutive
 Diagonal
Consecutive
Vertices
Angles
 Interior
 Exterior A
T
The name of this pentagon is PENTA.
Convex vs. Concave Polygons

Convex Polygons:

A polygon is convex
if no diagonal is
outside the polygon

Concave Polygons:

A polygon is concave
if at least one
diagonal is outside
the polygon
Sides
Name
Sides
Names of Polygons
Name
3
Triangle
8
Octagon
4
Quadrilateral
9
Nonagon
5
Pentagon
10
Decagon
6
Hexagon
12
Dodecagon
7
Heptagon
n
n-gon
DEFN: Regular Polygon

A polygon is regular if . . .
It is convex
Not
Equilateral
or
 It is equilateral
Not
Equilateral
Regular
or
Not?
Not!!
Regular
or
Not?
Not!!
YES

Regular or Not?
Equiangular
Equilateral
– all sides are the
same length
 Itis
equiangular

 Equiangular
measure
– all angles are the same
DEFN: Perimeter of a Polygon

Find perimeter
The
the perimeter
of a of
polygon
PENTA.
is the sum of
all sides.
N
6 in
E
Bet you’ve
never heard that
6 in one before
T
5 in
P

5 in
7 in
A
Perimeter = 5+6+6++5+7=29 inches
Perimeter revisited…
 To
find perimeter for a polygon in a
coordinate plane
Remember,
perimeter is the sum of the
I told you, this
lengths of all sides. . .
formula would be
Find the length (or measure)
of each
used all year.
..
side
 You
may have to use the distance formula
distance =
( x2  x1 )  ( y2  y1 )
2
2
Example
Find the perimeter of PQR if P(-5, 1), Q(-1,
4) say
and
Please
3,
R(-6, -8).
Please say
Perimeter = sum of all sides
How many sides does a triangle have?
3
So we have to find the length of 3 sides.
Oh, yes. . . The distance formula—3 times.
Find PQ, QR, and PR using the distance formula.
Have you learned. . .
How to identify and name polygons?
 Find perimeters of polygons?
 Assignment: Worksheet 1.6
