Sum of the Interior Angles in a Quadrilateral


Connect vertex A to each of the other vertices in the quadrilateral with a segment by moving the red sliders to the right

What did we just do?

By drawing segments that connect vertex A to all the other vertices, we have broken up this quadrilateral into triangles! Now connecting point A to point B and then point A to point C didn't really do anything, since they were already connected. That means we were only able to draw in one line that wasn't already there. We call segment AC a diagonal of the quadrilateral.

Think About and Answer the Following Questions

1. What do you remember about the sum of the angles in a triangle?

1. How many sides does a quadrilateral have?

3. How many triangles were you able to create in the quadrilateral above?

4. What might you guess then would be the sum of all the angles in a quadrilateral? (Use you answers from questions #1 and #3)