show that $\lim _ { z \to 0 } f(z)$ does not exist where :
$(1) f(z)= \frac {Re z}{z} : Z \neq 0 \downarrow
2. $\frac{{\text{Re} (z)}}{z} = \frac{{x^2 - xyi}}{{x^2 + y^2 }}$