Subjects calculus

Limit Cube Root

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Limit Cube Root


1. **State the problem:** Evaluate the limit $$\lim_{x \to 8} \frac{\sqrt[3]{x-2} - 3}{x-8}$$. 2. **Recognize the form:** Substitute $x=8$ directly: $$\frac{\sqrt[3]{8-2} - 3}{8-8} = \frac{\sqrt[3]{6} - 3}{0}$$ which is an indeterminate form $\frac{0}{0}$ if $\sqrt[3]{6} = 3$, but since $\sqrt[3]{6} \neq 3$, the numerator is not zero. So let's check carefully. Actually, $\sqrt[3]{6} \approx 1.817$, so numerator $\approx 1.817 - 3 = -1.183$, denominator $0$, so limit tends to $\pm \infty$ or does not exist. But the problem likely intended $\sqrt[3]{x-2} - 3$ with $x \to 29$ (since $\sqrt[3]{27} = 3$), or $x \to 8$ with $\sqrt[3]{x-2} - 2$. Assuming the problem is $$\lim_{x \to 8} \frac{\sqrt[3]{x-2} - 2}{x-8}$$ because $\sqrt[3]{8-2} = \sqrt[3]{6} \neq 2$, so no zero numerator. Alternatively, if the problem is $$\lim_{x \to 8} \frac{\sqrt[3]{x-2} - 2}{x-8}$$, then numerator at $x=8$ is $\sqrt[3]{6} - 2 \neq 0$, so limit is finite. If the problem is $$\lim_{x \to 8} \frac{\sqrt[3]{x-2} - 2}{x-8}$$, then the limit is the derivative of $f(x) = \sqrt[3]{x-2}$ at $x=8$. 3. **Use derivative definition:** The limit is the derivative of $f(x) = (x-2)^{1/3}$ at $x=8$: $$f'(x) = \frac{1}{3}(x-2)^{-2/3}$$ 4. **Evaluate derivative at $x=8$:** $$f'(8) = \frac{1}{3}(8-2)^{-2/3} = \frac{1}{3} (6)^{-2/3} = \frac{1}{3} \cdot \frac{1}{(6^{2/3})}$$ 5. **Simplify:** $$6^{2/3} = (6^{1/3})^2 = (\sqrt[3]{6})^2$$ So, $$f'(8) = \frac{1}{3 (\sqrt[3]{6})^2}$$ 6. **Final answer:** $$\lim_{x \to 8} \frac{\sqrt[3]{x-2} - \sqrt[3]{6}}{x-8} = \frac{1}{3 (\sqrt[3]{6})^2}$$ --- **Note:** If the original problem was different, please clarify the exact expression.