This middle school level math
interactive was developed for NCTM's Illuminations website to help students
learn about the relationship between the number of sides and the sum of the interior angles of
polygons.
Students start by selecting a
polygon (triangle, quadrilateral, pentagon, hexagon, heptagon or octagon)
located in the lower part of the screen.
They can then
click and drag the vertices to reshape it. As the figure changes, the angle
measures will automatically update in the table on the right.
For triangles and quadrilaterals, you can also play an
animated movie by clicking on the blue button in the lower right corner. This movie illustrates how the angle sum
of a triangle is always 180 degrees and the angle sum of a quadrilateral is
always 360 degrees.
Ideas for Exploration:
Ask students to
reshape the triangles and quadrilaterals. Have them also play the animated
movie by clicking on the blue button in the lower right corner. Ask them if
they notice a different result for different shapes.
Have your students then use the applet
to examine pentagons, hexagons, heptagons and octagons, too. Ask them if they
notice a pattern and ask them to see if they can find a formula that relates
the number of sides to the sum of the interior angle measures.
Grade
Levels: Grades 6-8
Tip for whole class
instruction: Project this
free math applet onto your interactive whiteboard and have you students click
and drag the vertices as they try to find a relationship between the number of
sides and the sum of the interior angles.
Resources: If you like this
applet, you can find more ideas on how to use it on the
NCTM Illuminations
website.