Dale Copy of Sum of Exterior Angle of Polygon

- Author:
- Dan Dale, Alfred Estberg

Use the applet below. Check the box next to triangle and then slide the Dilate slider. What do you notice about the 3 exterior angles of a triangle? Now check the box next to quadrilateral and then slide the Dilate slider. What do you notice about the 4 exterior angles of a quadrilateral? Do the same for pentagon, hexagon, and pentadecagon. Are there any similarities?

Note 2 things about exterior angles of polygons: 1) their sum is always 360 degrees; and 2) each exterior angle is supplementary to it’s adjacent interior angle.

1) To find the number of degrees for each exterior angle of a regular polygon, divide 360 degrees by the number of angles. Answer below.

2) To find x, write the equation setting up the 5 exterior angles to add up to 360 degrees. Answer below.

3) Be careful with this one. First find the value of x by setting up an equation where the 3 exterior angles add up to 360 degrees. Use that value of x and substitute it back in to find each exterior angle. Now you can find angle BCA (interior angle) by r

## Answer section.

1. 2. 3.