How is it convenient to obtain an image by reflection from a spherical mirror?

(N/A) We can take any two rays emanating from a point on an object,trace their paths,find their point of intersection,and thus,obtain the image of the point due to reflection at a spherical mirror.
In practice,however,it is convenient to choose any two of the following rays:
$(i)$ The ray from the point which is parallel to the principal axis. The reflected ray goes through the focus of the mirror.
$(ii)$ The ray passing through the centre of curvature of a concave mirror or appearing to pass through it for a convex mirror. The reflected ray simply retraces the path.
$(iii)$ The ray directed towards the pole of the mirror. The reflected ray follows the laws of reflection,making equal angles with the principal axis.
$(iv)$ The ray passing through the focus of a concave mirror or directed towards the focus of a convex mirror. The reflected ray becomes parallel to the principal axis.