CONCAVE MIRRORS!

Concave mirrors can form a *real image,*
bringing light to a focus. The geometrical relation is *(1/p)
+ (1/q) = (1/f) = (2/R),* where *p* is the object
distance, and *q* is the image distance, with *R*
the radius of curvature of the mirror surface and *f* the
focal length of the mirror.

To locate the image, draw any two of three
key rays. (1) A ray (P) parallel to the axis of symmetry, which
will be reflected through the focal point. (2) A ray (F) passing
through the focal point, which will be reflected parallel to the
symmetry axis, and (3) a ray (C) hitting the mirror in its
center, which will be reflected just as if it had hit a flat
mirror.

For convex mirrors it's easy to keep sign
conventions straight and check your answers if you just trace
the rays first. Note that convex mirrors always produce a
virtual image, just as plane mirrors do.