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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-
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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 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.
Describing Polygons Remember these prefixes
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.
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.
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.
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
Is this a right angle? Yes No
Good Thinking! No
Is this a right angle? Yes No
Well done! Yes
Is this a right angle? Yes No
Right!! No