General

Question 1

Formal limit def

Answer 1

$$\lim_{h \rightarrow 0} \frac{f(z+h)-f(z)}{h}$$

Question 2

partial y def

Answer 2

$$\lim_{h \rightarrow 0} \frac{\mathbf{f(a,b+h)}-f(a,b)}{h}$$

Question 3

partial x def

Answer 3

$$\lim_{h \rightarrow 0} \frac{\mathbf{f(a+h,b)}-f(a,b)}{h}$$