Let $f$ be the function defined by

$f(x)=\frac{x-3}{x^2-9}$

By computing the values of $f$ at

$2\mathrm{.}9,2\mathrm{.}99,2\mathrm{.}999$

and at

$3\mathrm{.}1,3\mathrm{.}01,3\mathrm{.}001$

estimate the value of

$\underset{x3}{lim}f(x)$