Geometric Shapes, Lines of Symmetry, & Right Angles 3rd Grade Strategies for Your Toolbox to Solve Geometry Problems

straight line segments 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

triangle – 3 sides; 3 angles Names of Polygons pentagon – 5 sides; 5 angles triangle – 3 sides; 3 angles circle – no sides 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 Sides Angles triangle 3 Square 4 Rectangle Pentagon 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!!! http://www.bbc.co.uk/schools/ks1bitesize/numeracy/shapes/fs.shtml

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 5 faces; 8 edges 2 faces; 3 edges 3 faces; 4 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. 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. 12

The line where a symmetrical object can be cut in half, AB, is called Line of Symmetry http://www.innovationslearning.co.uk/favicon.ico 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! Students will be given this on paper so that they can draw the line of symmetry.

Which of these faces is symmetrical?

Which of these is NOT symmetrical?

Right on Right angles

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.

Good Thinking! No

Is this a right angle? Yes No

Have another look.

Well done! Yes

Is this a right angle? Yes No

Have another look.

Right!! No

Great Job Today!!!