• If two inscribed angles mark off the same arc, the angles are equal in size.
• If an inscribed and a central angle mark off the same arc, the central angle is double the size of the inscribed angle.
• If the end points of a central angle can be connected with a diameter, the central angle is a right angle.
• The angle between a radius and a tangent is a right angle.
• The angle between the tangents drawn at the end points of two radii, and the angle between the radii make up a straight angle.

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