Substitution with a given u
Problem 4.488 · hard
Evaluate \( \displaystyle \int \frac{3 \cos{\left(\sqrt{x} \right)}}{\sqrt{x}}\, dx \) using the substitution \( \displaystyle u = \sqrt{x} \).
- \[ \frac{d}{d x} \sqrt{x} = \frac{1}{2 \sqrt{x}} \]So du = dx/(2√x).✓ Proved
- In terms of u the integral becomes ∫ 6*cos(u) du.Reviewed
- \[ \frac{d}{d u} 6 \sin{\left(u \right)} = 6 \cos{\left(u \right)} \]An antiderivative in u is 6*sin(u); differentiating confirms it.✓ Proved
- \[ 6 \sin{\left(\sqrt{x} \right)} \]Replace u by sqrt(x).✓ Proved
- \[ \frac{d}{d x} 6 \sin{\left(\sqrt{x} \right)} = \frac{3 \cos{\left(\sqrt{x} \right)}}{\sqrt{x}} \]Differentiating the answer returns the integrand.✓ Proved
Answer \( 6 \sin{\left(\sqrt{x} \right)} + C \)
✓ Nihil obstat Lines: 4 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 |
| 4 | ✓ Proved | sympy 1.14.0 | simplify(lhs - rhs) reduced to 0 |
| 5 | ✓ 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 | a difference quotient of the answer matches the integrand at x = 0.4, 0.9, 1.3 |
Reviewers
gpt-oss:20b: passqwen3.6:27b-mlx: pass — The solution correctly applies the substitution method, including the necessary factor of 2 from the differential, and verifies the result by differentiation.
Every verdict on record (4)
gpt-oss:20b: pass 2026-10-06qwen3.6:27b-mlx: pass 2026-10-06 — The solution correctly applies the substitution method, including the necessary factor of 2 from the differential, and verifies the result by differentiation.gpt-oss:20b: pass 2026-10-06qwen3.6:27b-mlx: pass 2026-10-06
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/indefinite_substitution, checked 2026-10-06 with SymPy 1.14.0.