13(a)Circle TheoremsEasy2 marksA, B and C are points on a circle with centre O. AOC is a straight line and M is the midpoint of AB. AB=6 cm and OM=4 cm.Work out OA.OA=cmGrade answerSolutionGrading criteria
13(b)Circle TheoremsMedium1 markGive a geometrical reason why angle ABC is 90∘.AThe angle between a tangent and a radius is 90∘BAngles in a triangle add up to 180∘CThe angle at the centre is twice the angle at the circumferenceDThe angle in a semicircle is 90∘EAngles in the same segment are equalFOpposite angles of a cyclic quadrilateral add up to 180∘GThe perpendicular from the centre to a chord bisects the chordHThe base angles of an isosceles triangle are equalGrade answerSolutionGrading criteria