Summary 7 major Circle Theorems





The angle subtended at the centre of a circle, by chord AB, is Twice the angle subtended at the circumference, by chord AB. 

Angles subtended by an arc in the same segment of a circle are Equal. 

Opposite angles of a cyclic quadrilateral add up to 180^{o} 





The angle in a semicircle is 90^{o}, or
The angle on a diameter is 90^{o} 

The angle betweeen a tangent and a radius drawn to the point of contact is 90^{o} 

From any point outside a circle just two tangents to the circle may be drawn, and they are of equal length from the point outside the circle to the point of contact. 





The angle between a tangent and a chord through the point of contact is Equal to the angle subtended by the chord in the alternate segment. 


