1. The sum of the interior angles in a regular polgyon is equal to 180(n-2), where n is the number of sides of the polygon.

The regular polygons displayed on the right are cyclic polygons.

Follow the directions provided at the bottom of the applet.

2. The opposite angles of a cyclic quadrilateral are supplementary (total 180^o). Therefore the angles in a cyclic quadrilateral total 360^o.

Cyclic quadrilateral example:

Interactive Activity

• Adjust A, B, C and D to form a cyclic quadrilateral ADBC.
• Notice <A + <B = 180^o and <C + <D= 180^o
• <A + <B + <C + <D will always equal 360^o.
• Hold the SHIFT key when you drag on the circumference of the circle to change the size of the circle.