First circle theorem - angles at the centre and at the circumference.
Second circle theorem - angle in a semicircle.
Third circle theorem - angles in the same segment.
Fourth circle theorem - angles in a cyclic quadlateral.
Fifth circle theorem - length of tangents.
Sixth circle theorem - angle between circle tangent and radius.
Seventh circle theorem - alternate segment theorem.
Eighth circle theorem - perpendicular from the centre bisects the chord