Average value of a function
Problem 4.753 · medium
Find the average value of \( \displaystyle f(x) = - x^{2} - x + 3 \) on \( \displaystyle [0, 1] \), and every \( \displaystyle c \) in the interval with \( \displaystyle f(c) = f_{\text{ave}} \).
- \[ \int\limits_{0}^{1} \left(- x^{2} - x + 3\right)\, dx = \frac{13}{6} \]The integral over the interval.✓ Proved
- \[ \frac{13}{6} \]Divide by the length of the interval.✓ Proved
- \[ - \frac{\sqrt{39}}{6} - \left(- \frac{1}{2} + \frac{\sqrt{39}}{6}\right)^{2} + \frac{7}{2} = \frac{13}{6} \]c = -1/2 + sqrt(39)/6 lies in [0, 1].✓ Proved
Answer \( f_{\text{ave}} = \frac{13}{6},\ c = - \frac{1}{2} + \frac{\sqrt{39}}{6} \)
Every line of this solution was proved by the computer algebra system SymPy. The answer was also checked a second way, without looking at the solution. The reviewers disagree about how one step is explained; every verdict is in the receipt.
The full receipt
| Line | Status | Checked by | Detail |
|---|---|---|---|
| 1 | ✓ Proved | sympy 1.14.0 | simplify(lhs - rhs) reduced to 0 |
| 2 | ✓ Proved | sympy 1.14.0 | simplify(lhs - rhs) reduced to 0 |
| 3 | ✓ Proved | sympy 1.14.0 | simplify(lhs - rhs) reduced to 0 |
| answer, a second way | ✓ Checked independently | sympy 1.14.0 + mpmath 1.3.0 | numerical quadrature for the average, and f evaluated at each c |
Reviewers
gpt-oss:20b: passqwen3.6:27b-mlx: inconclusive — reviewer returned a non-object
Every verdict on record (4)
gpt-oss:20b: pass 2026-10-09qwen3.6:27b-mlx: inconclusive 2026-10-09 — reviewer returned a non-objectgpt-oss:20b: pass 2026-10-09qwen3.6:27b-mlx: fail (error) 2026-10-09 — The solution fails to explicitly calculate the average value (integral divided by interval length) and incorrectly presents the verification of the root as the derivation of c. It also omits the second valid solution for c within the interval.
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/average_value, checked 2026-10-09 with SymPy 1.14.0.