Why do we need to use the sign convention again in the mirror equation while solving numericals when we know we have already used a convention while deriving the mirror equation? The question is not about the importance of sign conventions but why do we need to use the sign conventions twice? Doesn't the equation already include a sign convention?
1/u + 1/v = 1/ f
Or say, in the magification formula: height of image/ height of object = - (v/u)
Why do I need to bother about the signs ( -u or - v or +f) while using the above equations?