Investigating Mathematics with GeoGebra

Henrico County Public Schools

What is the sum of the interior angles of a polygon?

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

How many triangles is the figure divided?
What is the sum of the angles of a triangle?
What is the sum of the 6 angles in the figure?

How many triangles is the figure divided?
What is the sum of the angles in the center of the figure?
How many sides the figure have?

Investigation Steps

Click on the reset icon icon to reset the diagram.

 Figure 1 Close 
  1. Move any of the blue points to change the size or shape of the quadrilateral.

  2. What relationship exists between the opposite angles of a quadrilateral?

  3. Move the green point on the slider.

  4. What do you notice?
 Figure 2 Close 
  1. What is the sum of the interior angles of this polygon?

  2. What do think is the sum of the interior angles of any polygon?

  3. Can you explain your reasoning?

 More Hands-On Activities
Close 
  1. Explore Interior Angles 2

  2. Explore Interior Angles 3