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1. circle theorems

   • the angle in a semi circle is a right angle
   • the angle at the centre of a cirle is twice the angle subtended at any point on the circumference (subtended by the same arc or chord)
   • angles subtended by the same arc (ot chord) are equal
   • opposite angles of a cyclic quadrilateral add to 180 degrees
   • the angle between a tangent and chord is equal to the angle in the alternate segment
   • tangents from an external point are equal
   • the angle between a tangent and a radius is 90 degrees
   • the perpendicular from the centre of a circle bisects the chord

2. rules

   • angles at a point add to 360 degrees
   • angles in a triangle add to 180 degrees
   • angles on a straight line add to 180 degrees
   • angles in a quadrilateral add to 360 degrees

3. graph structures