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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!!!
http://www.bbc.co.uk/schools/ks1bitesize/numeracy/shapes/fs.shtml
3-Dimensional Shapes3-dimensional shapes have length, width, and height.
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.
http://www.innovationslearning.co.uk/favicon.ico
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.
Right Angles• A right angle is an angle
measuring 90 degrees. • The following angles are both
right angles.