I have the following equation
Given $$\lim_{x\to 2}\frac{2-x}{x^2-4}$$
using substitution we know that both the top and the bottom solve to $\frac{0}{0}$ this means that (per my text book and this is where I am lost) that the denominator is a factor of the numerator (it seems the numerator is a factor here...).
The above can be rewritten as
$$\frac{x-2}{(2-x)(x+2)}$$
cancel out the common factors
$$\frac{1}{x+2}$$
which solves to $\frac{1}{4}$
which is totally not right, as my answer key tells me that it is $-\frac{1}{4}$
Somewhere along the lines I am missing a key step.
In the comments, you said the question actually was
$$\lim_{x\to 2}\frac{2-x}{x^2-4}$$
Which since $2-x=-(x-2)$ rewrites to
$$-\lim_{x\to 2}\frac{x-2}{x^2-4}$$
This limit you already found as $1/4$ so
$$\lim_{x\to 2}\frac{2-x}{x^2-4}=-\frac14$$