Circle Radius Diameter Tangent Circumference

Angles subtended by the same chord are equal Chord

Angle subtended by the same chord at the centre is twice that at the circumference 2a a

Angle subtended by the same chord at the centre is twice that at the circumference 25 ○ What is the value of angle a? a a 50 ○ 2a = 180 ○ – 50 ○ 2a = 130 ○ a = 65 ○

Cyclic Quadrilaterals

The opposite angles of a cyclic quadrilateral add up to 180 ○ A cyclic quadrilateral is a quadrilateral whose vertices all lie on the circumference of a circle. a b Angle a + angle b = 1 80 ○

Angle in a semi circle equal 90 ○

Radius and Tangent 90\

The radius and tangent are at right angles o

Tangents to a Circle

Two tangents from the same point to a circle are equal

CIRCLES THE END THE END