∫Calc Practice

Absolute extrema on a closed interval

Problem 3.359 · hard

Find the absolute maximum and minimum values of \( \displaystyle f(x) = - x^{3} + \frac{3 x^{2}}{2} - 4 \) on \( \displaystyle [-2, 3] \).
  1. A continuous function on a closed interval has its extreme values at critical points or endpoints.
    Reviewed
  2. \[ \frac{d}{d x} \left(- x^{3} + \frac{3 x^{2}}{2} - 4\right) = - 3 x \left(x - 1\right) \]
    Differentiate and factor.✓ Proved
  3. Critical numbers inside [-2, 3]: 0, 1.
    Reviewed
  4. \[ \left. - x^{3} + \frac{3 x^{2}}{2} - 4 \right|_{\substack{ x=-2 }} = 10 \]
    f(-2).✓ Proved
  5. \[ \left. - x^{3} + \frac{3 x^{2}}{2} - 4 \right|_{\substack{ x=0 }} = -4 \]
    f(0).✓ Proved
  6. \[ \left. - x^{3} + \frac{3 x^{2}}{2} - 4 \right|_{\substack{ x=1 }} = - \frac{7}{2} \]
    f(1).✓ Proved
  7. \[ \left. - x^{3} + \frac{3 x^{2}}{2} - 4 \right|_{\substack{ x=3 }} = - \frac{35}{2} \]
    f(3).✓ Proved
  8. The largest value is 10 and the smallest is -35/2.
    Reviewed
Answer \( \text{max } 10 \text{ at } x=-2;\ \text{min } - \frac{35}{2} \text{ at } x=3 \)

✓ Nihil obstat Lines: 5 proved, 3 reviewed. The answer was also checked a second way, without looking at the solution. Reviewers found nothing wrong with the explanation.

The full receipt
LineStatusChecked byDetail
1Reviewedreviewers: gpt-oss:20b, qwen3.6:27b-mlxa sentence; read, not computed
2✓ Provedsympy 1.14.0simplify(lhs - rhs) reduced to 0
3Reviewedreviewers: gpt-oss:20b, qwen3.6:27b-mlxa sentence; read, not computed
4✓ Provedsympy 1.14.0simplify(lhs - rhs) reduced to 0
5✓ Provedsympy 1.14.0simplify(lhs - rhs) reduced to 0
6✓ Provedsympy 1.14.0simplify(lhs - rhs) reduced to 0
7✓ Provedsympy 1.14.0simplify(lhs - rhs) reduced to 0
8Reviewedreviewers: gpt-oss:20b, qwen3.6:27b-mlxa sentence; read, not computed
answer, a second way✓ Checked independentlysympy 1.14.0 + mpmath 1.3.0f sampled at 40,001 points across the interval reaches the same max and min

Reviewers

  • gpt-oss:20b: pass
  • qwen3.6:27b-mlx: pass
Every verdict on record (4)
  • qwen3.6:27b-mlx: pass 2026-10-03
  • gpt-oss:20b: pass 2026-10-03
  • qwen3.6:27b-mlx: pass 2026-10-03
  • gpt-oss:20b: pass 2026-10-03

Proved: SymPy reduced the difference between the two sides to zero. Checked independently: a separate method, named above, confirmed it. Checked numerically: the two sides agree at every sampled point, which is evidence, not proof. Reviewed: a model or a person read it; that is all a sentence can have. Solution by generator:structured/absolute_extrema, checked 2026-10-03 with SymPy 1.14.0.