By "limit definition", I assume you mean the derivative. We have
[tex]f'(c) = \displaystyle\lim_{x\to c}\frac{f(x)-f(c)}{x-c}[/tex]
For [tex]f(x)=\frac1{x-1}[/tex] and c = 2, we have
[tex]f'(2)=\displaystyle\lim_{x\to2}\frac{\frac1{x-1}-1}{x-2}[/tex]
[tex]f'(2)=\displaystyle\lim_{x\to2}\frac{\frac{1-(x-1)}{x-1}}{x-2}[/tex]
[tex]f'(2)=\displaystyle\lim_{x\to2}\frac{2-x}{(x-1)(x-2)}[/tex]
[tex]f'(2)=\displaystyle\lim_{x\to2}\frac1{1-x}=-1[/tex]
The tangent line to (2, 1) has slope -1. Using the point-slope formula, it has equation
y - 1 = - (x - 2)
y = - x + 3
