circle theorems

• the angle at the centre of the circle is twice the angle at the circumference of the circle from the same arc

  
• angles formed in a semi circle is always a right angle

  
• angles from the same arc in a segment is equal

  
• opposite angles of a cyclic quadraleteral adds up to 180 degrees

  
• the perpendicular line from the centre bisects of a circle to a chors bisects the chord

  
• the angle between the tangent and the radius where the tanget touches the circle is a right angle

  
• two tangents drawn from a point to the circle are equal

  
• the angle between a tangent and a chord is equal to the angle at the circumference in the alternate segment