\(\lim\limits_{x\rightarrow3^+}\dfrac{x^2-9}{x-3}=\)\(\lim\limits_{x\rightarrow3^+}\dfrac{\left(x-3\right)\left(x+3\right)}{x-3}=\)\(\lim\limits_{x\rightarrow3^+}x+3=6\)
\(\lim\limits_{x\rightarrow3^-}4x-5=7\)
\(\Rightarrow\lim\limits_{x\rightarrow3^+}f\left(x\right)\ne\)\(\lim\limits_{x\rightarrow3^-}f\left(x\right)\)
\(\Rightarrow f\left(x\right)\) không liên tục tại \(x=3\)
\(\Rightarrow\) Không tồn tại \(\lim\limits_{x\rightarrow3}f\left(x\right)\)