does concave mirror have a -ve value of distance of image ( di ) or +ve value of di ?

Question

sidsiddhartha · Answer

it can be both +ve and _ve 
if u consider (di) is +ve then the image is a real and located on the object's side of the mirror
and if (di) is -ve then
 image is a virtual and located behind the mirror

anonymous · Answer

|dw:1405803713104:dw||dw:1405803937603:dw|Like what sidsiddhartha said, if the object is farther than the focal length (do > f), then the image is in front of the mirror and inverted.  If the object is closer than the focal length (do < f), then the image is behind the mirror and upright.  Just remember the mirror equations: $$1/d_o + 1/d_i = 1/f$$$$d_o/d_i = -h_o/h_i$$.

Sorry for the poor quality images.