How to algebraically manipulate a limit of the form $\tfrac00$
Factoring can help us evaluate a limit. For example, we already
looked at the limit $$\lim_{x \to 1} \frac{x^2-1}{x-1}$$ Since
$x^2-1 = (x-1)(x+1)$, we have $$\lim_{x \to 1} \frac{x^2-1}{x-1} =
\lim_{x \to 1} \frac{(x-1)(x+1)}{x-1} = \lim_{x\to 1} (x+1) = 2.$$
Canceling the factors of $x-1$ from the numerator and denominator
is OK for all values of $x$ except $x=1$.
However, we're only looking at what happens when $x$ is close to 1, not
equal to 1, so the cancellation makes sense.