Geometric Shapes, Lines of Symmetry, & Right Angles

3 rd 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  Polygons are 2 dimensional Dimensions are length, width, and height Shapes formed by straight line segments that don’t cross

Names of Polygons triangle – 3 sides; 3 angles circle – no sides pentagon – 5 sides; 5 angles rectangle – 4 sides; 4 angles square – 4 equal sides; 4 equal angles

Describing Polygons A polygon is named according to the number of sides and angles that it has.

Name triangle Square Rectangle Pentagon Sides Angles 3 3 4 4 5 4 4 5

Describing Polygons Remember these prefixes Prefix Meaning tri quad penta hexa hepta octa nona deca 3 4 5 6 7 8 9 10

Let’s Practice!!!

http://www.bbc.co.uk/schools/ks1bitesize /numeracy/shapes/fs.shtml

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

3-Dimensional Shapes

3-Dimensional Shapes

Figure Out the Number of Sides & Edges Solid Patterns 6 faces; 12 edges 6 faces; 12 edges 3 faces; 4 edges 5 faces; 8 edges 2 faces; 3 edges

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 http://www.innovat

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The line where a symmetrical object can be cut in half, AB, is called the line of symmetry.

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

Yes

Is this a right angle?

No

Have another look.

Yes

Yes

Is this a right angle?

No

Have another look.

Good Thinking!

No

Yes

Is this a right angle?

No

Have another look.

Well done!

Yes

Yes

Is this a right angle?

No

Have another look.

No Right!!