Integrals of absolute values
Problem 4.890 · easy
Evaluate \( \displaystyle \int_{-1}^{2} \left| 2 x - 2 \right| dx \).
- \[ 2 x - 2 \]The integrand is zero at x = 1.✓ Proved
- Between those zeros the sign does not change; where it is negative, |p(x)| = −p(x).Reviewed
- \[ \int\limits_{1}^{2} \left(2 x - 2\right)\, dx + \int\limits_{-1}^{1} \left(2 - 2 x\right)\, dx = 5 \]Integrate each piece and add.✓ Proved
Answer \( 5 \)
✓ Nihil obstat Lines: 2 proved, 1 reviewed. 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 | Reviewed | reviewers: gpt-oss:20b, qwen3.6:27b-mlx | a sentence; read, not computed |
| 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 of |p(x)| |
Reviewers
gpt-oss:20b: passqwen3.6:27b-mlx: pass — The solution correctly identifies the split point at x=1, handles the absolute value by splitting the integral into regions where the expression is positive and negative, and computes the correct result.
Every verdict on record (4)
gpt-oss:20b: pass 2026-10-11qwen3.6:27b-mlx: pass 2026-10-11 — The solution correctly identifies the split point at x=1, handles the absolute value by splitting the integral into regions where the expression is positive and negative, and computes the correct result.gpt-oss:20b: pass 2026-10-11qwen3.6:27b-mlx: pass 2026-10-11 — The solution correctly identifies the split point at x=1 and applies the definition of absolute value to split the integral into two parts with correct bounds and integrands. The final calculation is correct.
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_value_integral, checked 2026-10-11 with SymPy 1.14.0.