\(\lim\limits_{x\rightarrow3^-}\dfrac{\sqrt{x^2-7x+12}}{\sqrt{9-x^2}}\)
\(=\lim\limits_{x\rightarrow3^-}\sqrt{\dfrac{\left(x-3\right)\left(x-4\right)}{\left(3-x\right)\left(3+x\right)}}\)
\(=\lim\limits_{x\rightarrow3^-}\sqrt{\dfrac{4-x}{3+x}}\)
\(=\sqrt{\dfrac{4-3}{3+3}}=\sqrt{\dfrac{1}{6}}=\dfrac{1}{\sqrt{6}}\)