Centers of mass and centroids
Problem 5.203 · medium
Find the centroid of the region bounded by \( \displaystyle y = 5 - x \) and \( \displaystyle y = 0 \) for \( \displaystyle 0 \le x \le 2 \).
- \[ \int\limits_{0}^{2} \left(5 - x\right)\, dx = 8 \]The area.✓ Proved
- \[ \int\limits_{0}^{2} x \left(5 - x\right)\, dx = \frac{22}{3} \]The moment about the y-axis.✓ Proved
- \[ \int\limits_{0}^{2} \frac{\left(5 - x\right)^{2}}{2}\, dx = \frac{49}{3} \]The moment about the x-axis: ∫ ½(top² − bottom²) dx.✓ Proved
- \[ \left[\begin{matrix}\frac{11}{12}\\\frac{49}{24}\end{matrix}\right] \]Divide each moment by the area.✓ Proved
Answer \( (\bar{x}, \bar{y}) = \left(\frac{11}{12}, \frac{49}{24}\right) \)
✓ Nihil obstat 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. Reviewers found nothing wrong with the explanation.
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 |
| 4 | ✓ 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 of each moment |
Reviewers
gpt-oss:20b: passqwen3.6:27b-mlx: pass — The solution correctly identifies the formulas for the area and moments, sets up the integrals with the correct bounds and integrands, and performs the division to find the centroid coordinates. The algebraic results are verified as correct.
Every verdict on record (4)
qwen3.6:27b-mlx: pass 2026-10-04 — The solution correctly identifies the formulas for the area and moments, sets up the integrals with the correct bounds and integrands, and performs the division to find the centroid coordinates. The algebraic results are verified as correct.gpt-oss:20b: pass 2026-10-04qwen3.6:27b-mlx: pass 2026-10-04 — The solution correctly identifies the formulas for area and moments, and the algebraic results are correct. The final centroid coordinates match the stated answer.gpt-oss:20b: pass 2026-10-04
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/center_of_mass, checked 2026-10-04 with SymPy 1.14.0.