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Definite integrals by substitution

Problem 4.909 · medium

Evaluate \( \displaystyle \int_{0}^{2} 3 x \left(x^{2} + 2\right)^{4}\, dx \).

Let u = x**2 + 2; then du = 2*x dx, which is in the integrand up to a constant.
Reviewed
\[ \left. x^{2} + 2 \right|_{\substack{ x=0 }} = 2 \]
The lower limit in u.✓ Proved
\[ \left. x^{2} + 2 \right|_{\substack{ x=2 }} = 6 \]
The upper limit in u.✓ Proved
\[ \int\limits_{2}^{6} \frac{3 u^{4}}{2}\, du = \frac{11616}{5} \]
Integrate in u between the new limits; no back-substitution needed.✓ Proved

Answer \( \frac{11616}{5} \)

✓ Nihil obstat Lines: 3 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	Reviewed	reviewers: gpt-oss:20b, qwen3.6:27b-mlx	a sentence; read, not computed
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 the original integral

Reviewers

gpt-oss:20b: pass
qwen3.6:27b-mlx: pass — The solution correctly applies u-substitution, properly adjusts the differential and limits, and computes the definite integral accurately.

Every verdict on record (4)

qwen3.6:27b-mlx: pass 2026-10-11 — The solution correctly applies u-substitution, properly adjusts the differential and limits, and computes the definite integral accurately.
gpt-oss:20b: pass 2026-10-11
gpt-oss:20b: pass 2026-10-11
qwen3.6:27b-mlx: pass 2026-10-11 — The solution correctly applies the method of u-substitution, including the proper adjustment of the differential (du = 2x dx implies x dx = du/2) and the transformation of integration limits. 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/definite_substitution, checked 2026-10-11 with SymPy 1.14.0.