Tìm \(\lim\limits_{x\rightarrow0}\dfrac{4x}{\sqrt{x+9}-3}\) .
\(6\).\(12\).\(18\).\(24\).Hướng dẫn giải:Cách 1: \(\lim\limits_{x\rightarrow0}\dfrac{4x}{\sqrt{x+9}-3}=\lim\limits_{x\rightarrow0}\dfrac{4x\left(\sqrt{x+9}+3\right)}{x}\)\(=\lim\limits_{x\rightarrow0}\dfrac{4\left(\sqrt{x+9}+3\right)}{1}=24\)