Giới hạn \(\mathop {\lim \to 3} - 9}}{{x - 3}}\) bằng

* Hướng dẫn giải

\(\begin{array}{l}\mathop {\lim }\limits_{x \to 3} \frac{{{x^2} - 9}}{{x - 3}} = \mathop {\lim }\limits_{x \to 3} \frac{{\left( {x - 3} \right)\left( {x + 3} \right)}}{{x - 3}}\\ = \mathop {\lim }\limits_{x \to 3} \left( {x + 3} \right) = 3 + 3 = 6\end{array}\)