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Angles in a Triangle


Angela Wenger

What is the sum of the angles in the interior of a triangle?

To find the sum of the angles in any triangle I need to construct a triangle using GSP and label each vertex.




Now that I have constructed my triangle, I need to measure each angle within the triangle. I can do this by using the measuring tool in GSP.



After measuring the interior angles I added the angles together and discovered a sum of 180 degrees.

If I go back to my figure and drag vertex A around, the measures of the angles change, but their sum does not. Which brings me to the following conclusion; the sum of the angles of a triangle equals 180 degrees.


Extension: Create a new sketch using GSP and draw a quadrilateral and find the sum of the interior angles. Is it always the same?

Click here to draw quadrilateral

Author & Contact
Angela Wenger

Link(s) to resources, references, lesson plans, and/or other materials
Click here to access GSP drawing of my triangle