Geometric Shapes, Lines of Symmetry, &

Right Angles

3rd Grade Strategies for Your Toolbox to Solve Geometry Problems

2-Dimensional Shapes• 2-dimensional – having only 2

dimensions (usually width and height) and no thickness

Dimensions are length,

width, and height

Polygons are 2- dimensional

Shapes formed by straight line segments

that don’t cross

Names of Polygons

triangle – 3 sides; 3 angles

pentagon – 5 sides; 5 angles

rectangle – 4 sides; 4 angles

square – 4 equal sides; 4 equal angles

circle – no sides

Describing Polygons

A polygon is named according to the

number of sides and angles that it has.

Name Sides Angles

triangle 3 3

Square 4 4

Rectangle 4 4

Pentagon 5 5

Describing Polygons Remember these prefixes

Prefix Meaning

tri 3

quad 4

penta 5

hexa 6

hepta 7

octa 8

nona 9

deca 10

Let’s Practice!!!

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3-Dimensional Shapes3-dimensional shapes have length, width, and height.

3-Dimensional Shapes

3-Dimensional Shapes

Figure Out the Number of Sides & Edges

6 faces; 12 edges

3 faces; 4 edges

5 faces; 8 edges

6 faces; 12 edges

2 faces; 3 edges

Solid Patterns

A shape is symmetrical if you can fold it in half and both sides match exactly.

This shape is symmetrical because if you folded it on the line, both

sides would match!

This shape is NOT symmetrical. Why not?

If you fold this shape in half along the line AB, is does not match up exactly. Both sides are triangles, but they are not symmetrical.

Line of Symmetry

The line where a symmetrical object can be cut in half, AB, is

calledthe line of symmetry.

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Let’s Practice!

Try it yourself – Draw a line of symmetry on each figure!

Which of these faces is symmetrical?

Which of these is NOT symmetrical?

What is an angle?• Two rays that share the same

endpoint form an angle. The point where the rays intersect is called the vertex of the angle. The two rays are called the sides of the angle.

Here are some examples

of angles.

Right Angles• A right angle is an angle

measuring 90 degrees. • The following angles are both

right angles.

Is this a right angle?

Yes No

Have another

look.

Yes

Is this a right angle?

Yes No

Have another

look.

No

Good Thinking!

Is this a right angle?

Yes No

Have another

look.

Yes

Well done

!

Is this a right angle?

Yes No

Have another

look.

NoRight!!