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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:

Since:

Use the fact that the angles of a triangle add up to 180° to find: