The user-friendly version of this content is available here.
The following content is copyright (c) 2009-2013 by Goods of the Mind, LLC.
This problem trains for: SAT-I, AMC-8.
In a regular pentagon inscribed in a circle with center O what is the measure of angle x?
Draw the radius OA:
Because the polygon is regular, the angle ∠COB is:
The triangle AOB is isosceles, since OA and OB are radii of the same circle. Therefore:
Use the fact that the angles of a triangle add up to 180° to find: