Derivative Cuberoot
1. **Statement of the problem:** Find the derivative of the function:
$$f(x) = \left(\sqrt[3]{4x^{2} - 5}\right)^{-1} = \frac{1}{(4x^{2} - 5)^{1/3}}$$
2. **Rewrite the function:** Using exponent notation,
$$f(x) = (4x^{2} - 5)^{-1/3}$$
3. **Apply the chain rule:** The derivative of $f(x) = u^{n}$ where $u = 4x^{2} - 5$ and $n = -\frac{1}{3}$ is
$$f'(x) = n u^{n-1} \cdot u'$$
4. **Calculate $u'$:**
$$u' = \frac{d}{dx}(4x^{2} - 5) = 8x$$
5. **Substitute values into the derivative formula:**
$$f'(x) = -\frac{1}{3} (4x^{2} - 5)^{-\frac{4}{3}} \cdot 8x$$
6. **Simplify the expression:**
$$f'(x) = -\frac{8x}{3} (4x^{2} - 5)^{-\frac{4}{3}}$$
This is the correct derivative.
7. **Check the incorrect derivative given:**
The provided derivative was
$$f'(x) = - \frac{1}{6x^{3}} \cdot (4x^{2} - 5)^{-\frac{2}{3}}$$
This is incorrect because the derivative does not have $x^{3}$ in the denominator and the exponent of $(4x^{2} - 5)$ is wrong.
**Final answer:**
$$\boxed{f'(x) = -\frac{8x}{3} (4x^{2} - 5)^{-\frac{4}{3}}}$$
This completes the differentiation process with detailed steps.