hi, im just a little bit stuck on this question. Use the definition of the derivative of a function to prove that the funtion f(z)=Im z is nowhere differentiable.

i know that f'(z)=lim f(z+delta(z))-f(z)/delta(z)

along the real axis, ive found the limit to be 1, bt along the imaginary axis ive also found this to be the case, so can anyone tell me where ive gone wrong.