Integral of \( \displaystyle \frac{\left(2 x + 1\right)^{2} + 1}{2 x \left(2 x + 1\right)} \)
Problem 4.795 · hard
Find \( \displaystyle \int \frac{\left(2 x + 1\right)^{2} + 1}{2 x \left(2 x + 1\right)} \, dx \). (Omit the constant of integration.)
- \[ \int \left(\frac{2 x + 1}{2 x} + \frac{1}{2 x \left(2 x + 1\right)}\right)\, dx \]algebra simplifySplit the fraction using the numerator's terms. Cancel common terms in the first part of the integrand.✓ Proved
- \[ = \int \left(1 + \frac{1}{2 x} + \frac{1}{2 x \left(2 x + 1\right)}\right)\, dx \]algebraDivide the numerator by the denominator in the first term.✓ Proved
- \[ = \int 1\, dx + \int \frac{1}{2 x}\, dx + \int \frac{1}{2 x \left(2 x + 1\right)}\, dx \]linearityDistribute the integral across the sum.✓ Proved
- \[ = \int 1\, dx + \int \frac{1}{2 x}\, dx + \int \left(- \frac{1}{2 x + 1} + \frac{1}{2 x}\right)\, dx \]rewriteUse partial fraction decomposition on the third term.✓ Proved
- \[ = \int 1\, dx + 2 \int \frac{1}{2 x}\, dx - \int \frac{1}{2 x + 1}\, dx \]linearity simplifySplit the integral of the decomposed term. Combine the identical integral terms.≈ Checked numerically
- \[ = x + \ln{\left(2 x \right)} - \frac{\ln{\left(2 x + 1 \right)}}{2} \]antiderivative simplifyIntegrate each term separately. Simplify the coefficients.✓ Proved
- \[ = x + \ln{\left(2 x \right)} - \ln{\left(\sqrt{2 x + 1} \right)} \]rewriteRewrite the division by 2 as a square root inside the logarithm.✓ Proved
- \[ = x + \ln{\left(\frac{2 x}{\sqrt{2 x + 1}} \right)} \]simplifyUse logarithmic properties to combine the terms into a single logarithm.≈ Checked numerically
Answer \( x + \ln{\left(x \right)} - \frac{\ln{\left(x + \frac{1}{2} \right)}}{2} + C \)
Lines: 9 proved, 3 checked numerically. The answer was also checked a second way, without looking at the solution. The reviewers disagree about how one step is explained; every verdict is in the receipt.
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 undefined where x = 0 undefined where 2*x + 1 = 0 |
| 3 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 undefined where x = 0 undefined where 2*x + 1 = 0 |
| 4 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 undefined where x = 0 undefined where 2*x + 1 = 0 |
| 5 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 undefined where x = 0 undefined where 2*x + 1 = 0 |
| 6 | ≈ Checked numerically | sympy 1.14.0 | sympy 1.14.0: simplify left -log(x + 1/2)/2 + log(2*x + 1)/2; numeric agreement only, at 24 of 24 sampled points undefined where x = 0 undefined where 2*x + 1 = 0 |
| 7 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 undefined where x = 0 undefined where 2*x + 1 = 0 |
| 8 | ✓ Proved | sympy 1.14.0 | lines differ by the constant -log(2) undefined where x = 0 undefined where 2*x + 1 = 0 log is undefined for non-positive arguments |
| 9 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 log is undefined for non-positive arguments |
| 10 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 log is undefined for non-positive arguments |
| 11 | ≈ Checked numerically | sympy 1.14.0 | sympy 1.14.0: simplify left log(x) - log(x/sqrt(2*x + 1)) - log(2*x + 1)/2; numeric agreement only, at 24 of 24 sampled points log is undefined for non-positive arguments undefined where 2*x + 1 = 0 |
| answer | ≈ Checked numerically | sympy 1.14.0 | sympy 1.14.0: final line against the stated answer: simplify left -log(x) + log(x/sqrt(2*x + 1)) + log(x + 1/2)/2 + log(2); numeric agreement only, at 24 of 24 sampled points log is undefined for non-positive arguments |
| 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: fail (misleading) — Step 10 incorrectly rewrites log(2*x + 1)/2 as log(sqrt(2*x + 1)), which is only valid when 2*x + 1 > 0. The correct identity is log(|2*x + 1|)/2 = log(sqrt(|2*x + 1|)). This omission of absolute values makes the solution invalid for domains where 2*x + 1 < 0.
Every verdict on record (4)
gpt-oss:20b: pass 2026-10-10qwen3.6:27b-mlx: fail (misleading) 2026-10-10 — Step 10 incorrectly rewrites log(2*x + 1)/2 as log(sqrt(2*x + 1)), which is only valid when 2*x + 1 > 0. The correct identity is log(|2*x + 1|)/2 = log(sqrt(|2*x + 1|)). This omission of absolute values makes the solution invalid for domains where 2*x + 1 < 0.gpt-oss:20b: pass 2026-10-10qwen3.6:27b-mlx: fail (style) 2026-10-10 — [domain objection, downgraded to style] Step 10 is mathematically incorrect: log(2*x + 1)/2 is not equal to log(sqrt(2*x + 1)) without absolute values, and the transformation is unnecessary and confusing. Step 11 combines logs incorrectly by ignoring the domain restrictions and absolute values required for log(a) - log(b) = log(a/b). The final answer form is also inconsistent with the stated answer provided in the task description.
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 2026-10-10 with SymPy 1.14.0.