If a line is drawn from the centre of a circle perpendicular to a chord, then it bisects the chord.
The perpendicular bisector of a chord passes through the centre of the circle.
Angles in the same segment of a circle are equal.
If a quadrilateral is cyclic, then the opposite angles are supplementary.
If two tangents are drawn from the same point outside a circle, then they are equal in length.
The angle between a tangent to a circle and a chord drawn from the point of contact is equal to an angle in the alternate segment.
Summary
Theorems as per Grade 11 CAPS document