Question
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Find the intervals on which the graph of \( f \) is concave upward, the intervals on which the graph of \( f \) is concave downward, and the inflection points. \( f(x)=x^{16}+3 x^{2} \)

Ask by Elliott Bryant. in the United States
Mar 11,2025

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Answer

The graph of \( f(x) = x^{16} + 3x^2 \) is concave upward everywhere, with no intervals where it's concave downward or inflection points.

Solution

**Step 1. Compute the first derivative** We start with \[ f(x) = x^{16} + 3x^2. \] The first derivative is \[ f'(x) = 16x^{15} + 6x. \] **Step 2. Compute the second derivative** Differentiate \( f'(x) \) to obtain \[ f''(x) = 240x^{14} + 6. \] **Step 3. Determine the concavity** The concavity of the graph is determined by the sign of \( f''(x) \). Notice that for any real number \( x \), \[ x^{14} \geq 0, \] so \[ 240x^{14} \geq 0. \] Thus, \[ f''(x) = 240x^{14} + 6 \geq 6. \] Since \( 6 > 0 \), it follows that \[ f''(x) > 0 \quad \text{for all } x. \] **Step 4. Conclude Concavity and Inflection Points** - The graph is concave upward on the interval \((-\infty, \infty)\) because \( f''(x) > 0 \) for all \( x \). - There are no intervals where the graph is concave downward. - An inflection point occurs where \( f''(x) \) changes sign. Since \( f''(x) \) is always positive and never equals zero, there are no inflection points. **Final Answer:** - Concave upward on: \((-\infty, \infty)\) - Concave downward on: *None* - Inflection points: *None*

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Beyond the Answer

To determine the concavity of the function \( f(x) = x^{16} + 3x^{2} \), we first need to find the second derivative \( f''(x) \). 1. Calculate the first derivative: \[ f'(x) = 16x^{15} + 6x \] 2. Calculate the second derivative: \[ f''(x) = 240x^{14} + 6 \] To find the intervals of concavity and the inflection points, we need to analyze \( f''(x) \): 3. Set \( f''(x) = 0 \) to find possible inflection points: \[ 240x^{14} + 6 = 0 \\ 240x^{14} = -6 \\ x^{14} = -\frac{1}{40} \] Since \( x^{14} \) is always non-negative, there are no solutions for this equation. Thus, \( f''(x) \) does not change sign. 4. Now, let's analyze the sign of \( f''(x) \): - For all \( x \) (since \( 240x^{14} \) is always non-negative and \( +6 \) is positive), we conclude: - \( f''(x) > 0 \) for all \( x \). From above analysis, we can characteristically conclude: - The graph of \( f \) is concave upward on the entire real line \( (-\infty, \infty) \). - Since there are no points where \( f''(x) = 0 \) or changes sign, there are no inflection points. So, in summary: - The function is concave upward on \( (-\infty, \infty) \). - The function is never concave downward. - There are no inflection points.

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