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Maxima & Minima · Question 52 of 80

Question 52

MediumOriginal question

What is the greatest value of f(x)=x3−3xf(x) = x^{3} - 3 x on [−2,3][-2, 3]?

Options for question 52

Show the answer and explanation
CorrectNot quiteAnswer D

Correct answer: D

Explanation

  1. Critical points inside the interval: f′(x)=3(x−1)(x+1)=0f'(x) = 3 \left(x - 1\right) \left(x + 1\right) = 0 at x=−1,1x = -1, 1.

  2. Compare ff there and at the two ends: f(−2)=−2f(-2) = -2, f(3)=18f(3) = 18, f(−1)=2f(-1) = 2, f(1)=−2f(1) = -2.

  3. The greatest value is 1818.

Worth noting

A local extremum is not always the greatest or least value: the ends of the interval must be checked too.

Concept
Greatest and least values on a closed interval
Typical time
90 s
Your time
—
The rule this testsGreatest and least values on an interval
Practise this chapter →

Ten questions from Maxima & Minima, at your own pace.

Practise this chapter →

Ten questions from Maxima & Minima, at your own pace.