Answer
$-\infty$
Work Step by Step
$\lim _{x\rightarrow 5^-}\dfrac {\sqrt {25-x^{2}}}{x-5}\dfrac {=\dfrac {d}{dx}\left( \sqrt {25-x^{2}}\right) }{\dfrac {d}{dx}\left( x-5\right) }=\dfrac {\dfrac {-2x}{2\sqrt {25-x^{2}}}}{1}=-\dfrac {x}{\sqrt {25-x^{2}}}=-\dfrac {5}{\sqrt {25-5^{2}}}=-\infty $