Substitution with a given u
Problem 4.933 · hard
Evaluate \( \displaystyle \int \frac{5 e^{4 x}}{e^{4 x} + 1}\, dx \) using the substitution \( \displaystyle u = e^{4 x} + 1 \).
- \[ \frac{d}{d x} \left(e^{4 x} + 1\right) = 4 e^{4 x} \]So du = 4e^(4x) dx.✓ Proved
- In terms of u the integral becomes ∫ 5/(4*u) du.Reviewed
- \[ \frac{d}{d u} \frac{5 \ln{\left(u \right)}}{4} = \frac{5}{4 u} \]An antiderivative in u is 5*log(u)/4; differentiating confirms it.✓ Proved
- \[ \frac{5 \ln{\left(e^{4 x} + 1 \right)}}{4} \]Replace u by exp(4*x) + 1.✓ Proved
- \[ \frac{d}{d x} \frac{5 \ln{\left(e^{4 x} + 1 \right)}}{4} = \frac{5 e^{4 x}}{e^{4 x} + 1} \]Differentiating the answer returns the integrand.✓ Proved
Answer \( \frac{5 \ln{\left(e^{4 x} + 1 \right)}}{4} + C \)
✓ 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, handles the constant factor from the differential, and verifies the result. No errors or misleading statements found.
Every verdict on record (4)
gpt-oss:20b: pass 2026-10-12qwen3.6:27b-mlx: pass 2026-10-12 — The solution correctly applies the substitution method, handles the constant factor from the differential, and verifies the result. No errors or misleading statements found.gpt-oss:20b: pass 2026-10-12qwen3.6:27b-mlx: pass 2026-10-12 — The solution correctly applies the substitution method, handles the constant factor from the differential, and verifies the result by differentiation.
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 2026-10-12 with SymPy 1.14.0.