all DISTANCE ate measured from pole of the mirror as origin.
distance measured in the same direction as that of incident LIGHT are taken as positive .if it is OPP then take distance negative.
the object distance us always negative
if an image is formed behind a concave mirror the image distance is positive but if the image is formed in FRONT of mirror then the image distance is negative
the focal length of concave mirror is considered negative
the height of an object is always considered positive