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Lesson Materials

Approximate the Area of a Circle

READ the instructions on the right and INTERACT with the GeoGebra applet below.

Sorry, the GeoGebra Applet could not be started. Please install Java 1.4 (or later) to use this page.

Objective

6.12 The student will
a) solve problems involving the circumference and/or area of a circle when given the diameter or radius; and b) derive approximations for pi (∏) from measurements for circumference and diameter, using concrete materials or computer models.

Investigation Steps

Click on the reset icon icon to reset the diagram.

 Directions Close 

Move the green point half-way across the slider.

  1. What the sum of the bases of the triangles that compose the regular polygon?

  2. What is the height of those triangles?

  3. After verifying the transformation of a regular polygon of 16 sides, imagine another one of 360 sides.
 Directions 2 Close 

Move the green point on the slider completely to the right.

  1. What area it will be equivalent the area of a many-sided regular polygon?

  2. Using this information, what would be a formula for finding the area of a circle?

 Other Web Sites Close 
  1. LearnAlberta

    2. Choose Circle Area topic
    from Shape and Space column.

  2. Inscribed Polygons

    3. Find approximate area of
    circles by inscribing polygons.

 Puzzles & Problems tangram Close 
From Math Forum: A cow is tethered in a field using a 50-ft. rope tied to one corner of the outside of a 20 ft. by 10 ft. barn. What is the total area that the cow is capable of grazing?