\(\mathop {\lim }\limits_{x \to  + \infty } \left( {\sqrt {x + 1}  - \sqrt {x - 7} } \right)\) bằng:

* Hướng dẫn giải

\(\mathop {\lim }\limits_{x \to  + \infty } \left( {\sqrt {x + 1}  - \sqrt {x - 7} } \right) = \mathop {\lim }\limits_{x \to  + \infty } \frac{{\left( {x + 1} \right) - \left( {x - 7} \right)}}{{\sqrt {x + 1}  + \sqrt {x - 7} }} = \mathop {\lim }\limits_{x \to  + \infty } \frac{8}{{\sqrt {x + 1}  + \sqrt {x - 7} }} = 0\)