There are actually different types of mirrors. They are named like their shape: planar, parabolic, elliptical, spherical.
Planar mirrors are like the ones in homes. They reflect light so that the image appears to be on the other side of the mirror just as far away as the object is.
Problems involving curved mirrors usually use spherical concave mirrors and are the easiest to solve. Spherical mirrors have 2 special points, the center and the focus. The center is the point where each spot on the mirror is the same distance away in all directions. All light that comes straight in (parallel to the center axis) bounces out through the focus.
First, you draw a diagram with the object standing on top of a line that runs through the center of the mirror. Then you can draw a line from the top of the object parallel to the center straight into the mirror. That ray bounces out through the focus, so you can continue that line down through the focus. Now, draw another line from the top of the object straight through the focus to the mirror. This is like the opposite of before, so the light will go straight back (parallel to the center). The last line goes from the top of the object strait through the center point and to the mirror. Because this mirror is spherical, it will hit the mirror and go back the way it came, to the top of the original object.
Now, you should see that all 3 lines you drew cross at one point. This is the top of the image that the mirror makes. It is below the center line, which means that the image is inverted.
Check out the Physics Classroom
for some more hints on mirrors.
(republished on 07/29/06)