Derivative of \( \displaystyle x \ln{\left(2 x + 2 \right)} - x + \ln{\left(x + 1 \right)} \)
Problem 2.354 · hard Beautiful
Differentiate \( \displaystyle f(x) = x \ln{\left(2 x + 2 \right)} - x + \ln{\left(x + 1 \right)} \).
- \[ \frac{d}{d x} \left(x \ln{\left(2 x + 2 \right)} - x + \ln{\left(x + 1 \right)}\right) \]Start with the derivative of the function.✓ Proved
- \[ = - \frac{d}{d x} x + \frac{d}{d x} x \ln{\left(2 x + 2 \right)} + \frac{d}{d x} \ln{\left(x + 1 \right)} \]sumApply the sum rule to differentiate each term separately.✓ Proved
- \[ = \frac{d}{d x} x \ln{\left(2 x + 2 \right)} + \frac{d}{d x} \ln{\left(x + 1 \right)} - 1 \]constantThe derivative of x is 1.✓ Proved
- \[ = x \frac{d}{d x} \ln{\left(2 x + 2 \right)} + \ln{\left(2 x + 2 \right)} \frac{d}{d x} x + \frac{d}{d x} \ln{\left(x + 1 \right)} - 1 \]productApply the product rule to the first term.✓ Proved
- \[ = x \frac{d}{d x} \ln{\left(2 x + 2 \right)} + \ln{\left(2 x + 2 \right)} + \frac{d}{d x} \ln{\left(x + 1 \right)} - 1 \]constantThe derivative of x is 1.✓ Proved
- \[ = \frac{x \frac{d}{d x} \left(2 x + 2\right)}{2 x + 2} + \ln{\left(2 x + 2 \right)} - 1 + \frac{\frac{d}{d x} \left(x + 1\right)}{x + 1} \]chainApply the chain rule to the logarithmic terms.✓ Proved
- \[ = \frac{2 x}{2 x + 2} + \ln{\left(2 x + 2 \right)} - 1 + \frac{1}{x + 1} \]derivative algebraDifferentiate the inner functions. Simplify the products.✓ Proved
- \[ = \frac{x}{x + 1} + \ln{\left(2 x + 2 \right)} - 1 + \frac{1}{x + 1} \]algebraSimplify the fraction (2*x)/(2*x + 2) by dividing numerator and denominator by 2.✓ Proved
- \[ = \ln{\left(2 x + 2 \right)} \]algebra algebra simplifyCombine the fractions with the same denominator. Simplify the fraction (x + 1)/(x + 1) to 1. Combine the remaining terms.✓ Proved
Answer \( \log{\left(2 x + 2 \right)} \)
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. 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 log is undefined for non-positive arguments |
| 3 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 log is undefined for non-positive arguments |
| 4 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 log is undefined for non-positive arguments |
| 5 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 log is undefined for non-positive arguments |
| 6 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 log is undefined for non-positive arguments undefined where x + 1 = 0 undefined where 2*x + 2 = 0 |
| 7 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 log is undefined for non-positive arguments undefined where x + 1 = 0 undefined where 2*x + 2 = 0 |
| 8 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 log is undefined for non-positive arguments undefined where x + 1 = 0 undefined where 2*x + 2 = 0 |
| 9 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 log is undefined for non-positive arguments undefined where x + 1 = 0 undefined where 2*x + 2 = 0 |
| 10 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 log is undefined for non-positive arguments undefined where x + 1 = 0 |
| 11 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 log is undefined for non-positive arguments |
| 12 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 log is undefined for non-positive arguments |
| answer | ✓ Proved | sympy 1.14.0 | final line against the stated answer: simplify(a - b) reduced to 0 log is undefined for non-positive arguments |
| answer, a second way | ✓ Proved | sympy 1.14.0 | SymPy differentiated f directly and got the stated answer |
Reviewers
gpt-oss:20b: passdeepseek-r1:70b: passqwen3.6:27b-mlx: pass — The solution correctly applies differentiation rules step-by-step, adhering to the one-change-per-step constraint. All labels are appropriate for the transformations performed.
Every verdict on record (10)
qwen3.6:27b-mlx: pass 2026-09-20 — The solution correctly applies differentiation rules step-by-step, adhering to the one-change-per-step constraint. All labels are appropriate for the transformations performed.gpt-oss:20b: pass 2026-09-20qwen3.6:27b-mlx: pass 2026-09-20 — The solution correctly applies differentiation rules step-by-step, with each step changing only one aspect of the expression and using valid labels from the fixed vocabulary.gpt-oss:20b: fail (error) 2026-09-20 — Step 6 applies the chain rule to two logarithmic terms in a single line, violating the one‑rule‑per‑step rule. Additionally, step 5 labels the replacement of Derivative(x,x) with 1 as a "constant" rule, when it should be a "derivative" rule.qwen3.6:27b-mlx: pass 2026-09-19 — The solution correctly applies differentiation rules step-by-step, adhering to the one-change-per-step constraint. The labels accurately reflect the operations performed, and the algebraic simplifications are correct.deepseek-r1:70b: pass 2026-09-19gpt-oss:20b: pass 2026-09-19qwen3.6:27b-mlx: pass 2026-09-19deepseek-r1:70b: pass 2026-09-19gpt-oss:20b: pass 2026-09-19
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 2026-09-26 with SymPy 1.14.0.