criteri de derivades

lim[h-->0][ (h/h)·( f(x+h)+(-1)f(x) )/( g(x+h)+(-1)g(x) ) ] = lim[h-->0][ ( f(x+h) )/( g(x+h) ) ] = ...
... ( f(x)/g(x) ) <==> ( f(x) = 0  & g(x) = 0 )