MG 2.1
Identify, describe, and classify polygons (including pentagons,
hexagons, and octagons).
UNDERLYING SKILLS AND CONCEPTS:
visualize 2-dimensional figures;
sort 2-dimensional figures;
vocabulary for geometry
Name and Classify Polygons
Shape Names Tell
the Number of Sides
triangles
3 sides
quadrilaterals
4 sides
pentagons
5 sides
hexagons
6 sides
Next come the quadrilaterals:
They all have 4 sides.
septagons
7 sides
octagons
8 sides
A polygon is named by the number of
sides it has.
nonagons
9 sides
decagons
10 sides
The simplest polygon is a triangle:
a triangle has 3 sides and 3 angles.
Name: Triangle Quadrilateral Pentagon Hexagon Septagon Octagon Nonagon
Number
3
4
5
6
7
8
9
of sides:
E x am p l E
Which of these is NOT a polygon? Explain why.
A
B
C
D
E
F
C is not a polygon. It does not have straight sides.
E is not a polygon because it is not closed.
F is not a polygon. Not all its sides are straight line segments.
page 266
Chapter 23 – Lesson 1
C – © CSL Associates, Inc. All rights reserved.
K
a
ey Ide
A polygon is a closed figure made
of line segments.
Polygons have at least three
angles and at least three
line segments.
Name
P RAC T I C E
Put the letter of the figure by its shape name.
If there are none, write none.
1. triangle
none
2. quadrilateral A, D, E
3. pentagon
4. hexagon
5. septagon
6. octagon
7. nonagon
C – © CSL Associates, Inc. All rights reserved.
8. decagon
B
F
none
G
none
H
A
9. Which of these are NOT
triangles?
C and D
B
E
C
F
D
G
H
10. Which of these are NOT
quadrilaterals?
A
Explain why. C because one
Explain why.
side is not straight; and D
Because it has 5 sides.
because it is not closed.
Math
Reasoning
Spatial Visualization
MR 2.3
11. Cut out these two shapes. Show 2 polygons you can make
by putting 2 of these pattern pieces together.
square, parallelogram
Chapter 23 – Lesson 1
page 267
MCX94.HW.CL.G3.FM&Lesson.v211
8/3/04
13:56
Page 178
Name
…at home!
P RAC T I C E
Put the letter of the figure by its shape name.
If there are none, write none.
1. triangle
none
2. quadrilateral H, E, D
4. hexagon
5. septagon
6. octagon
7. nonagon
8. decagon
G
C
none
B
none
A
A
9. Which of these are NOT
triangles?
C and D
B
E
C
F
D
G
H
10. Which of these are NOT
quadrilaterals?
A
Explain why. C because one
Explain why.
side is not straight; and D
Because it has 6 sides.
because it is not closed.
Math
Reasoning
Spatial Visualization
MR 2.3
11. Cut out four of this shape. Show 2 polygons you can make
by putting these 4 pieces together.
page 178
Home Resource and Homework
Chapter 23 Lesson 1
C – © CSL Associates, Inc. All rights reserved.
3. pentagon
MCX94TEG3Ch01_32.v8.9.3 2/21/01 14:50 Page 491
Name
P RAC T I C E
Put the letter of the figure by its shape name.
If there are none, write none.
1. triangle
none
2. quadrilateral A, D, E
3. pentagon
4. hexagon
5. septagon
6. octagon
7. nonagon
C – © CSL Associates, Inc. All rights reserved.
8. decagon
B
F
none
G
none
H
A
B
E
C
F
D
G
H
10. Which of these are NOT
quadrilaterals?
A
9. Which of these are NOT
triangles?
C and D
Explain why. C because one
Explain why.
side is not straight; and D
Because it has 5 sides.
because it is not closed.
Math
Reasoning
Spatial Visualization
MR 2.3
11. Cut out these two shapes. Show 2 polygons you can make
by putting 2 of these pattern pieces together.
square, parallelogram
Chapter 23 – Lesson 1
Student Book Page
page 267
Name
…at home!
P RAC T I C E
Put the letter of the figure by its shape name.
If there are none, write none.
1. triangle
none
2. quadrilateral H, E, D
4. hexagon
5. septagon
6. octagon
7. nonagon
8. decagon
G
C
none
B
none
A
A
9. Which of these are NOT
triangles?
C and D
B
E
C
F
D
G
H
10. Which of these are NOT
quadrilaterals?
A
Explain why. C because one
Explain why.
side is not straight; and D
Because it has 6 sides.
because it is not closed.
Math
Reasoning
Spatial Visualization
MR 2.3
11. Cut out four of this shape. Show 2 polygons you can make
by putting these 4 pieces together.
page 178
Home Resource and Homework
Chapter 23 Lesson 1
C – © CSL Associates, Inc. All rights reserved.
3. pentagon