Exercise · ZW-CONCAVITY-AND-INFLECTION-POINTS-007 · ★★☆ Intermediate
On which interval is the graph of \(f(x)=x^{3}\) concave up?
Choose one option.
Show answer
- A. \((0,\infty)\)
Explanation
We have \(f''(x)=6x\), which is positive only when \(x>0\). So the graph is concave up on \((0,\infty)\).
Review the concept: Concavity and inflection points
If \(f^{\prime\prime}>0\) on an interval, the graph is concave up; if \(f^{\prime\prime}<0\), concave down. An inflection point is where the concavity changes, and there \(f^{\prime\prime}(c)=0\) or does not exist.
\[\begin{gathered}f''>0\ \Rightarrow\ \text{concave up}\\ f''<0\ \Rightarrow\ \text{concave down}\end{gathered}\]
More practice problems: concavity and inflection points
- ZW-CONCAVITY-AND-INFLECTION-POINTS-001 At which value of x does f(x)=x^3 - 6 x^2 + 9 x have its inflection point?
- ZW-CONCAVITY-AND-INFLECTION-POINTS-002 At which value of x does f(x)=x^3 - 3 x^2 + 1 have its inflection point?
- ZW-CONCAVITY-AND-INFLECTION-POINTS-003 At which values of x does f(x)=x^4 - 6 x^2 have inflection points?
- ZW-CONCAVITY-AND-INFLECTION-POINTS-004 For f(x)=x^4, f''(0)=0. Does f have an inflection point at x = 0?
- ZW-CONCAVITY-AND-INFLECTION-POINTS-005 What does f''(x)>0 on an interval indicate?
- ZW-CONCAVITY-AND-INFLECTION-POINTS-006 What is an inflection point of a graph?
- ZW-CONCAVITY-AND-INFLECTION-POINTS-008 Where is the inflection point of f(x)=x^3-3x?
- ZW-CONCAVITY-AND-INFLECTION-POINTS-009 At which values of x does f(x)=x^4-4x^3 have inflection points?
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