5.1 In a triangle, an exterior angle is the sum of the other two interior angles.
5.2 In a circle, an inscribed angle is half as big as the corresponding central angle.
5.3 If A is a point on a circle and AC is tangent to the circle at A and B is any other point on the circle, then angle BAC is half of angle AOB. The deflection angle is half of the central angle.
5.4 If AB is a chord of a circle, O is the center, and D is a point on AB, then the following are equivalent
5.5 If AB and AC are tangents to a circle from point A where B and C are the points of tangency, then AB = AC
5.6 If the endpoints of a diameter of a circle are joined to a point on the circle, a right triangle will be formed.
