<s>[INST] Consider the funcition and find an expression Consider the function $f(x) = \frac{2}{x-1}$ and find an expression for $\frac{f(x+h)-f(x)}{h}$ and simplify where he cannot be equal to $0$.
 [/INST] $\require{cancel}$
$$f(x) = \frac 2{x - 1}$$ 
$$\frac{f(x + h) - f(x)}{h} = \frac{\dfrac{2}{(x + h) - 1} - \dfrac {2}{x - 1}}{h}$$
Multipy numerator and denominator by $(x + h - 1)(x - 1)$
$$\begin {align}\frac{\dfrac{2}{(x + h) - 1} - \dfrac {2}{x - 1}}{h} \cdot \frac{ \dfrac{(x + h - 1)(x - 1)}{1}}{(x + h - 1)(x - 1)} & = \frac{2(x - 1) - 2(x + h - 1)}{h(x+h - 1)(x - 1)}\\ \\ & = \dfrac{-2\cancel{h}}{\cancel{h}(x+h + 1)(x-1)}\end{align}$$
After canceling the common factor, you're done.
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