I'm trying to think this out, but I just can't get it to make any sense. Let f be continuous on [a,b] (a<b) and differentiable on (a,b). If f(a) = 0 and abs(f'(x)) <= c*abs(f(x)) on (a,b), show that abs(f'(x)) <= (c^2)*(x-a)*abs(f(d)), a < d < x. Does anyone know what is needed to be done here? Thanks in advance.