Final answer:
The size of the magnification of a single convex mirror can vary depending on the object distance. It can be positive or negative depending on whether the image formed is upright or inverted.
Step-by-step explanation:
The size of the magnification of a single convex mirror can vary depending on the object distance. It is not always positive or always negative. The magnification can be positive or negative depending on whether the image formed is upright or inverted. When the object is placed beyond the focal point of a convex mirror, the image formed is virtual and upright, but smaller than the object. The magnification is positive in this case. However, when the object is placed between the mirror and the focal point, the image formed is virtual, upright, and larger than the object. The magnification is negative in this case.