(a) According to sign convention, distances measured against the direction of incident light are taken as negative such that Object distance (u) for a concave mirror or convex mirror is always negative.

(b) According to sign convention, distances measured in the same direction as that of incident light are taken as positive and distances measured against the direction of incident light are taken as negative such that if the image is formed on the left side of the mirror, then the image distance (v) will be negative and if the image is formed on the right side of the mirror, then the image distance (v) will be positive.

(c) According to sign convention, distances measured in the same direction as that of incident light are taken as positive such that Image distances (v) for a convex mirror is always positive.