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 \(PQ\).
Solution:
\(\angle OPO'\) \(=\) \(^\circ\)
\(OO' = \) \(cm\)
\(PQ = \) \(cm\)