I have another question that I thought I was doing correctly. Can anyone explain this to me please?
In separate experiments, an object is placed 12.0 cm in front of two different mirrors: a flat mirror and a convex mirror. The image formed by the convex mirror is 4.0 cm closer to the mirror than the image formed by the plane mirror. Determine the focal length of the convex mirror.
The image distance of the flat mirror is 12cm. The image distance of the convex mirror is 8cm. Since the convex mirror forms virtual images this would be -8cm. Using the thin lens equation,
1/f = 1/do + 1/di. 1/12 - 1/8 = -0.0416
1/-0.0416 = -24cm = f
I have the answer for this question and it says that the image distance is -24cm and that the focal length is 4.8cm.