In the given figure, a circle is inscribed in a quadrilateral \(ABCD\) in which \(\angle B = 90^\circ\). If \(AD =13 \ cm\), \(AB = 21 \ cm\) and \(DS =4 \ cm\), then determine the radius of the circle.
In quadrilateral \(OPBQ\),
\(BQ=\)
\(OQ=\)
All the angles in the quadrilateral \(OPBQ\) is \(^\circ\)
Thus, the quadrilateral \(OPBQ\) is a
Hence, radius \(=\) \(cm\)