Maths, Physics Revision Physicss Maths Physics Physics A Level Physics Home Maths Maths Revision hut Angles in circles All angles in a semi circle are 90 o The angle subtended at the centre is twice  the angle at the circumference A tangent is a line  which touches the  circle and makes an angle Of  900  with the radius of the circle A A The angle between the tangent and a chord is equal to the  angle subtended in the opposite segment Centre of circle radius Chord Segment Diameter (twice the radius) Sector Parts of a circle Click here for Parts of circle Back to top Circumference Or 𝜋 �� X D Area of a circle  =  𝜋 X r2