Two chords AP and QM of a circle intersect internally at a point R. If AR = 21 cm, RP = 9 cm, and PQ = 21 cm, then find MR.
6 cm
When two chords of a circle intersect internally, then the products of the lengths of segments are equal.
i.e. AR×RP=MR×RQ⇒14×9=MR×21⇒14×921=MR
∴ MR = 6 cm