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

2. 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

3. 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

4. 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

5. Describing Polygons Remember these prefixes Prefix Meaning tri 3 quad4
penta 5
hexa 6
hepta 7
octa 8
nona 9
deca 10

6. Let’s Practice!!!

7. 3-dimensional shapes have length, width, and height.

8. 3-Dimensional Shapes

9. 3-Dimensional Shapes

10. 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

11. 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!

12. 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

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

14. Let’s Practice!

17. 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.

18. Which of these faces is symmetrical?

19. Which of these is NOT symmetrical?

20. Right on
Right angles

21. 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.

22. Here are some examples
of angles.

23. Right Angles A right angle is an angle measuring 90 degrees.
The following angles are both right angles.

24. Is this a right angle?
Yes No

25. Have another look.

26. Yes

27. Is this a right angle?
Yes No

28. Have another look.

29. Good
Thinking! No

30. Is this a right angle?
Yes No

31. Have another look.

32. Well done!
Yes

33. Is this a right angle?
Yes No

34. Have another look.

35. Right!! No

36. Great Job Today!!!