Using \(XQ\) as base, two triangles \(\triangle PXQ\) and \(\triangle QRX\) are formed. \(PQ = PX\), and \(XR = QR\). Verify that \(\angle PQR = \angle PXR\).
Proof:
Join \(PR\), then consider the triangles \(PQR\) and \(PXR\).
\(PQ = \)
\(XR = \)
\(PR =\) ()
Thus \(\triangle PQR \cong \triangle PXR\) (by congruence rule).
By CPCT, \(\angle PQR = \angle\) .