1. Classifying
Two-Dimensional
Figures

2. Classifying 2-Dimensional Figures
Let’s look at some vocabulary
terms before we start classifying figures.
Two-dimensional – having a width and a height but flat like a piece of paper.
Polygon
Two-dimensions
Polygon – a two-dimensional shape made up of straight lines that are closed.
One-dimension
Three-dimensions

3. Polygons are either regular or irregular.
Classifying 2-Dimensional Figures
Polygons are either regular or irregular.
This is a regular pentagon because ALL of its sides and angles are congruent.
Congruent – having the same measure
Hash marks indicate sides with the same length.
Angle arcs indicate angles of the same measure.
This is an irregular pentagon because some of its sides and angles
are not congruent.

4. Here is a list of the most basic polygons:
Classifying 2-Dimensional Figures
Here is a list of the most basic polygons:
3-sided
Triangle
7-sided
Septagon
Quadrilateral
4-sided
8-sided
Octagon
Pentagon
5-sided
9-sided
Nonagon
6-sided
Hexagon
10-sided
Decagon

5. Classifying
Quadrilaterals

6. A main group of polygons are
Properties of Quadrilaterals
A main group of polygons are
the quadrilaterals.
All quadrilaterals have:
4 sides
4 angles (that add up to 360°)

7. Classifying Quadrilaterals
We classify quadrilaterals based on whether or not they have certain properties:
How many sets of parallel sides it has
Parallel Line -Two lines on the same plane that will never cross. They are always the same distance apart.

8. Classifying Quadrilaterals
We classify quadrilaterals based on whether or not they have certain properties:
The number of congruent sides it has
Congruent – having the same measure, indicated by hash lines
These sides are congruent
These sides are congruent

9. Classifying Quadrilaterals
We classify quadrilaterals based on whether or not they have certain properties:
If it contain right angles
Right angles = 90 degrees, indicated by a square in the corner

10. Classifying Quadrilaterals
Let’s classify quadrilaterals from those with the fewest properties to those with the most properties.
Quadrilateral with one pair of parallel sides
Quadrilateral with no parallel or congruent sides
Trapezoid
Basic Quadrilateral

11. Classifying Quadrilaterals
Two pairs of parallel sides
Opposite sides congruent
A parallelogram
Four 90° angles □ □ □ □
Parallelogram
Rectangle
By definition, rectangles are considered parallelograms.
Why can’t parallelograms be classified as rectangles?
Parallelograms do not have 4 90 degree angles.

12. Classifying Quadrilaterals
A parallelogram
A rectangle
A rhombus
A parallelogram
4 congruent sides □ □
Rhombus □ □
Square
Why can we classify a square as a rectangle and a rhombus?
A square is a parallelogram with 4 right angles (rectangle)
A square is a parallelogram with 4 congruent sides (rhombus)

13. Trail 3 Classifying 2-Dimensional Figures Higher Grounds ITALIA Work F
Name each of the following polygons. 2.
YIELD
WORD BANK
triangle
pentagon
rectangle
parallelogram
right triangle
octagon
trapezoid
square
rhombus
Higher Grounds
Coffee 1.
trapezoid
triangle
parallelogram
Work
Zone 4. F FA
Future Farmers
of America 3.
pentagon 5.
ITALIA
World Cup
2014
Trail 3 6.
trapezoid
triangle

14. Classifying 2-Dimensional Figures
Answer the following questions.
1. What do the “hash marks” indicate on the sides of polygons?
Hash marks indicate that those side lengths are congruent.
2. What’s the difference between a regular and irregular polygon?
A regular polygon has sides and angles that are all congruent. An irregular polygon does not.
3. By definition, we can classify all rectangles as parallelograms, but why can’t we classify parallelograms as rectangles?
A rectangle has two pairs of parallel sides and two pairs of congruent sides as defined by a parallelogram. However, a rectangle has four 90° right angles which is not included in the definition of a parallelogram.
4. What’s the difference between an obtuse angle and an acute angle?

15. Classifying 2D Figures Match each term with one of the figures. B G F
1. Triangle _____ Rhombus _____ 3. Pentagon _____ 4. Trapezoid ________ E C D
5. Octagon _____ Parallelogram _____ 7. Quadrilateral _____ E A F C D
120° G B

16. Classifying
Triangles

17. There are just a few basic ways that we classify or name triangles!
Properties of Triangles
All triangles have:
3 sides
3 angles (that add up to 180°)
There are just a few basic ways that we classify or name triangles!

18. We classify or name triangles by their angles.
Classifying Triangles
We classify or name triangles by their angles.
< 90°
All angles
Acute Triangle □
One 90° angle
Right Triangle
One angle > 90°
Obtuse Triangle

19. We also classify triangles by their side lengths and angle measures.
Classifying Triangles
We also classify triangles by
their side lengths and angle measures.
3 congruent sides
All angles congruent
Equilateral Triangle
2 congruent sides
2 congruent angles
Isosceles Triangle
No congruent sides
No congruent angles
Scalene Triangle

20. Classify each triangle by ALL names that apply.
Name that Triangle!
Classify each triangle by ALL names that apply. 2.
____________________
Acute
Isosceles □ 1.
____________________ 3.
140°
____________________
Right
Isosceles
Obtuse
Scalene