In the given mirror
C – centre of the sphere to which the mirror is part of
F – focus of the mirror
P – pole of mirror
A – point on mirror
D – point on the principal axis
If a ray of light starts from C and is incident on A, then from which point the reflected ray will pass through?
C
CA will fall normally to the concave mirror, thus by laws reflection the angle of incidence is O and so the angle of reflection will be O. Hence the ray will retrace its path and pass through C (centre of curvature).