Polygons: Angles vs. Sides

Math Lesson Plan
Students will realize the relationship between the number of sides of a polygon and the sum of its angles.

Lesson Plan graphic

pattern blocks, overhead projector

  1. Using the overhead projector, make a polygon with pattern blocks—start with a 4-sided one.
  2. Trace the outside of the shape, then remove the blocks.
  3. Have students make their own outline of a 4-sided polygon using the same method. They can make theirs whatever shape they would like, as long as it has 4 sides.
  4. Using the tan pattern block pieces, measure the angles of the polygon you made. Do this by placing the pointy end of the tan pattern blocks in the corner (angle); continue inserting tan pattern blocks into this corner until it is covered. Do this for each corner and then add up the total number of blocks used. They should add up to 12.
  5. Have your students do the same with their polygons. They will also end up with 12.
  6. Then have your students work independently to make 5-sided polygons with the pattern blocks. They will do the same thing that they did with the 4-sided figures.
  7. Have them do this independently, adding one more side to their shape each time until you feel they have mastered it.
  8. Have students record their information in chart format: Angles vs. Sides. When students are finished, make a chart on the overhead to show what the students discovered.

Have students look at the chart and notice if there is a pattern. Ask your class why and how the knowledge of this polygon pattern is useful in the “real” world.

Notice which students did not get the correct angle counts for the polygons and those students that found a pattern before you brought up the idea. Which students were able to give some real-life uses for this knowledge?