47. Exemplar exercise problems XXI

Two circles with centres \(O\) and \(O'\) of radii \(3 \ cm\) and \(4 \ cm\), respectivley intersect at two points \(P\) and \(Q\) such that \(OP\) and \(O'P\) are tangents to the two circles. Find the length of the common chord \(PQ\).

 

\(PQ = \) \(cm\)