mirrors, if one moves the term to the right side of the equation to solve for , then the result is always a negative number, meaning that the image distance is negative--the image is virtual, located "behind" the mirror. This is consistent with the behavior described above.

For concave mirrors, whether the image is virtual or real depends on how large the object distance is compared to the focal length. If the term is larger than the term, then is positive and the image is real. Otherwise, the term is negative and the image is virtual.