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 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. NameSidesAngles triangle33 Square44 Rectangle44 Pentagon55

Describing Polygons Remember these prefixes PrefixMeaning tri3 quad4 penta5 hexa6 hepta7 octa8 nona9 deca10

Let’s Practice!!! /numeracy/shapes/fs.shtml

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

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 called the line of symmetry. ionslearning.co.uk /favicon.ico

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? YesNo

Have another look.

Yes

Is this a right angle? YesNo

Have another look.

No Good Thinking!

Is this a right angle? YesNo

Have another look.

Yes Well done!

Is this a right angle? YesNo

Have another look.

No Right!!