Average value of a function
Problem 4.758 · medium
Find the average value of \( \displaystyle f(x) = \sqrt{x} \) on \( \displaystyle [0, 4] \), and every \( \displaystyle c \) in the interval with \( \displaystyle f(c) = f_{\text{ave}} \).
- \[ \int\limits_{0}^{4} \sqrt{x}\, dx = \frac{16}{3} \]The integral over the interval.✓ Proved
- \[ \frac{4}{3} \]Divide by the length of the interval.✓ Proved
- \[ \frac{4}{3} \]c = 16/9 lies in [0, 4].✓ Proved
Answer \( f_{\text{ave}} = \frac{4}{3},\ c = \frac{16}{9} \)
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: fail (misleading) — The solution omits the crucial step that shows f(c)=f_ave for c=16/9; it merely states an identity without linking c to the function value, which could mislead a student into thinking the verification is complete.qwen3.6:27b-mlx: fail (error) — The solution fails to explicitly state the definition of average value or set up the equation f(c) = f_ave to solve for c. It merely asserts the final values without showing the necessary logical steps connecting the integral to the Mean Value Theorem for Integrals.
Every verdict on record (4)
gpt-oss:20b: fail (misleading) 2026-10-09 — The solution omits the crucial step that shows f(c)=f_ave for c=16/9; it merely states an identity without linking c to the function value, which could mislead a student into thinking the verification is complete.qwen3.6:27b-mlx: fail (error) 2026-10-09 — The solution fails to explicitly state the definition of average value or set up the equation f(c) = f_ave to solve for c. It merely asserts the final values without showing the necessary logical steps connecting the integral to the Mean Value Theorem for Integrals.gpt-oss:20b: pass 2026-10-09qwen3.6:27b-mlx: fail (error) 2026-10-09 — The solution fails to show the calculation for finding c (solving sqrt(c) = 4/3). It merely states the result and checks the bounds, omitting the necessary algebraic step.
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.