Exercise · ZW-ROLLES-THEOREM-006 · ★★☆ Intermediate
For \(f(x)=x^{3}-x\) on \([-1,1]\), which of these values satisfies \(f'(c)=0\) with \(c\in(-1,1)\)?
Choose one option.
Show answer
- A. \(\frac{1}{\sqrt{3}}\)
Explanation
Since \(f'(x)=3x^{2}-1\), solving \(3c^{2}-1=0\) gives \(c=\pm\frac{1}{\sqrt{3}}\), both in \((-1,1)\). The positive value is the one listed.
Review the concept: Rolle's theorem
If \(f\) is continuous on \([a,b]\), differentiable on \((a,b)\) and \(f(a)=f(b)\), there is at least one \(c\in(a,b)\) with \(f^{\prime}(c)=0\).
\[f(a)=f(b)\ \Rightarrow\ \exists\,c\in(a,b):\ f'(c)=0\]
More practice problems: rolle's theorem
- ZW-ROLLES-THEOREM-001 Verify Rolle's theorem for f(x)=x^2 - 4 x + 3 on [1,3] and find c with f'(c)=0.
- ZW-ROLLES-THEOREM-002 Verify Rolle's theorem for f(x)=sin x on [0,π] and find c with f'(c)=0.
- ZW-ROLLES-THEOREM-003 Which of these conditions is NOT a hypothesis of Rolle's theorem?
- ZW-ROLLES-THEOREM-004 In which of these cases do the hypotheses of Rolle's theorem NOT hold?
- ZW-ROLLES-THEOREM-005 If the hypotheses of Rolle's theorem hold on [a,b], what does the conclusion state?
- ZW-ROLLES-THEOREM-007 For f(x)=x^2 on [0,2], which c∈(0,2) satisfies f'(c)=(f(2)-f(0))/(2-0)?
- ZW-ROLLES-THEOREM-008 Which of these cases is continuous with f(a)=f(b), but has no c∈(a,b) with f'(c)=0?
- ZW-ROLLES-THEOREM-009 What does Rolle's theorem mean geometrically?