Integral of \( \displaystyle \left(3 x - 1\right) e^{3 x - 1} \)
Problem 4.169 · medium
Find \( \displaystyle \int \left(3 x - 1\right) e^{3 x - 1} \, dx \). (Omit the constant of integration.)
- \[ \int \left(3 x - 1\right) e^{3 x - 1}\, dx \]integralStart with the integral of the given function.✓ Proved
- \[ = \int \left(3 x e^{3 x - 1} - e^{3 x - 1}\right)\, dx \]linearityDistribute the exponential term.✓ Proved
- \[ = 3 \int x e^{3 x - 1}\, dx - \int e^{3 x - 1}\, dx \]linearitySplit the integral into two parts.✓ Proved
- \[ = x e^{3 x - 1} - 3 \int \frac{e^{3 x - 1}}{3}\, dx - \int e^{3 x - 1}\, dx \]partsApply integration by parts to the first integral term.✓ Proved
- \[ = x e^{3 x - 1} - 2 \int e^{3 x - 1}\, dx \]simplify algebraSimplify the expression. Combine the integral terms.✓ Proved
- \[ = x e^{3 x - 1} - \frac{2 e^{3 x - 1}}{3} \]antiderivative simplifyEvaluate the remaining integral. Final simplification.✓ Proved
Answer \( \left(x - \frac{2}{3}\right) e^{3 x - 1} + C \)
✓ 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 | line 1 is the problem as stated |
| 2 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 |
| 3 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 |
| 4 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 |
| 5 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 |
| 6 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 |
| 7 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 |
| 8 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 |
| answer | ✓ Proved | sympy 1.14.0 | final line against the stated answer: simplify(a - b) reduced to 0 |
| answer, a second way | ✓ Proved | sympy 1.14.0 | SymPy differentiated the stated antiderivative back to the integrand |
Reviewers
gpt-oss:20b: passqwen3.6:27b-mlx: pass
Every verdict on record (4)
qwen3.6:27b-mlx: pass 2026-09-29gpt-oss:20b: pass 2026-09-29qwen3.6:27b-mlx: pass 2026-09-29gpt-oss:20b: fail (style) 2026-09-29 — Step 4 applies two rules at once: it performs integration by parts and then multiplies the result by 3. Each step should change only one thing; this should be split into two separate steps.
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
gemma4:26b, checked 2026-09-29 with SymPy 1.14.0.