\(\text { Tính giới hạn } E=\lim\limits _{x \rightarrow 3} \frac{2-\sqrt{x+1} \cdot \sqrt[3]{x-2}}{2-\sqrt{x-2} \cdot \sqrt[3]{x+5}} \text { . }\)
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Lời giải:
Báo sai\(\begin{aligned} &\text { Ta có } E=\lim \limits _{x \rightarrow 3} \frac{2-\sqrt{x+1} \cdot \sqrt[3]{x-2}}{2-\sqrt{x-2} \cdot \sqrt[3]{x+5}}=\lim \limits _{x \rightarrow 3} \frac{2-\sqrt{x+1}-\sqrt{x+1}(\sqrt[3]{x-2}-1)}{2-\sqrt[3]{x+5}-\sqrt[3]{x+5}(\sqrt{x-2}-1)} \\ &=\lim \limits _{x \rightarrow 3} \frac{\frac{4-(x+1)}{2+\sqrt{x+1}}-\sqrt{x+1} \cdot \frac{(x-2)-1}{\sqrt[3]{(x-2)^{2}}+\sqrt[3]{x-2}+1}}{\frac{8-(x+5)}{4+\sqrt[3]{x+5}+\sqrt[3]{(x+5)^{2}}}-\sqrt[3]{x+5} \cdot \frac{(x-2)-1}{\sqrt{x-2}+1}}=\lim \limits _{x \rightarrow 3} \frac{-\frac{x-3}{2+\sqrt{x+1}}-\frac{(x-3) \sqrt{x+1}}{\sqrt[3]{(x-2)^{2}}+\sqrt[3]{x-2}+1}}{-\frac{1}{4+\sqrt[3]{x+5}+\sqrt[3]{(x+5)^{2}}}-\frac{(x-3) \sqrt[3]{x+5}}{\sqrt{x-2}+1}} \\ &=\lim \limits _{x \rightarrow 3} \frac{-\frac{1}{2+\sqrt{x+1}}-\frac{\sqrt{x+1}}{\sqrt[3]{(x-2)^{2}}+\sqrt[3]{x-2}+1}}{-\frac{1}{4+\sqrt[3]{x+5}+\sqrt[3]{(x+5)^{2}}}-\frac{\sqrt[3]{x+5}}{\sqrt{x-2}+1}}=\frac{-\frac{1}{4}-\frac{2}{3}}{-\frac{1}{12}-1}=\frac{11}{13} . \end{aligned} \)