Question:medium

Find the absolute maximum and minimum values of the function: \[ f(x) = 12x^{4/3} - 6x^{1/3}, \quad x \in [0, 1]. \]

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To find absolute extrema of a function on a closed interval, evaluate the function at critical points and endpoints, and compare the values.
Updated On: Jan 13, 2026
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Solution and Explanation

1. Compute the derivative of \( f(x) \). The function is \( f(x) = 12x^{4/3} - 6x^{1/3} \). Differentiating with respect to \( x \), we get \( f'(x) = 12 \cdot \frac{4}{3}x^{1/3} - 6 \cdot \frac{1}{3}x^{-2/3} \). Simplifying yields \( f'(x) = 16x^{1/3} - 2x^{-2/3} \). 2. Identify critical points by setting \( f'(x) = 0 \): \( 16x^{1/3} - 2x^{-2/3} = 0 \). Factorizing gives \( 2x^{-2/3}(8x - 1) = 0 \). This implies \( x^{-2/3} = 0 \) (invalid for \( x eq 0 \)) or \( 8x - 1 = 0 \). Solving \( 8x - 1 = 0 \) yields \( x = \frac{1}{8} \). 3. Evaluate \( f(x) \) at the critical point and endpoints. The critical point is \( x = \frac{1}{8} \). We evaluate \( f(x) \) at \( x = 0 \), \( x = 1 \), and \( x = \frac{1}{8} \). - For \( x = 0 \): \( f(0) = 12(0)^{4/3} - 6(0)^{1/3} = 0 \). - For \( x = 1 \): \( f(1) = 12(1)^{4/3} - 6(1)^{1/3} = 12 - 6 = 6 \). - For \( x = \frac{1}{8} \): \( f\left(\frac{1}{8}\right) = 12\left(\frac{1}{8}\right)^{4/3} - 6\left(\frac{1}{8}\right)^{1/3} \). We have \( \left(\frac{1}{8}\right)^{1/3} = \frac{1}{2} \) and \( \left(\frac{1}{8}\right)^{4/3} = \left(\frac{1}{2}\right)^4 = \frac{1}{16} \). Substituting these values: \( f\left(\frac{1}{8}\right) = 12 \cdot \frac{1}{16} - 6 \cdot \frac{1}{2} = \frac{3}{4} - 3 = -\frac{9}{4} \). 4. Determine maximum and minimum values. - \( f(0) = 0 \) - \( f(1) = 6 \) - \( f\left(\frac{1}{8}\right) = -\frac{9}{4} \) The absolute maximum value is \( f(1) = 6 \). The absolute minimum value is \( f\left(\frac{1}{8}\right) = -\frac{9}{4} \). Final Answer: - Absolute maximum value: \( 6 \) at \( x = 1 \). - Absolute minimum value: \( -\frac{9}{4} \) at \( x = \frac{1}{8} \).
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