Circles

A is a point at a distance 13 cm from the centre O of a circle of radius 5 cm. AP  and AQ  are  the  tangents  to  the  circle  at  P  and  Q.  If  a  tangent  BC  is drawn at a point R lying on the minor arc PQ to intersect AP at B and AQ at C, find the perimeter of the ∆ABC.