circle theorems (maths)

when a radius meets a tangent, the angle will always be 90 degrees

From a point outside a circle, 2 tangents can be drawn. from the point to where they touch the circle, they are equal in length

the angle subtended at the centre of the circle is double the angle at the circumference 

the angle in a semi circle is a right angle

angles in the same segment are equal

alternate segment theorem - the angle between a tanget and a chord is equal to the angle in the circumference in the alternate segment

the oppisite angles of a cyclic quadrilateral add up to 180 degrees