Sol. Construct the ray BAC and find point C (optical centre of the mirror (Fig. a). Pole P can be found by constructing the path of the ray APA' reflected : : the pole with the aid of symmetrical point A'. The position of the mirror focus F is determined by means of the usual construction of ray AMF parallel to the axis.

(Fig. a) (Fig. b)

This construction can also be used to find centre C of the mirror and pole P (Fig. b). The reflected ray BM will pass parallel to the optical axis of the mirror. For this reason, to find the focus, let us first determine point M at which straight line AM, parallel to the optical axis, intersects then mirror, and then extend BM to the point of intersection with the axis at the focus F.