Derivative of \( \displaystyle x \left(\ln{\left(4 x \right)} - 1\right) \)
Problem 2.376 · medium
Differentiate \( \displaystyle f(x) = x \left(\ln{\left(4 x \right)} - 1\right) \).
- \[ \frac{d}{d x} x \left(\ln{\left(4 x \right)} - 1\right) \]derivativeStart with the derivative of the function.✓ Proved
- \[ = x \frac{d}{d x} \left(\ln{\left(4 x \right)} - 1\right) + \left(\ln{\left(4 x \right)} - 1\right) \frac{d}{d x} x \]productApply the product rule.✓ Proved
- \[ = x \frac{d}{d x} \left(\ln{\left(4 x \right)} - 1\right) + \ln{\left(4 x \right)} - 1 \]derivativeDifferentiate the first part of the product.✓ Proved
- \[ = - x \frac{d}{d x} 1 + x \frac{d}{d x} \ln{\left(4 x \right)} + \ln{\left(4 x \right)} - 1 \]sumDistribute the derivative across the subtraction.✓ Proved
- \[ = x \frac{d}{d x} \ln{\left(4 x \right)} + \ln{\left(4 x \right)} - 1 \]derivative algebraDifferentiate the constant term. Simplify the zero term.✓ Proved
- \[ = \ln{\left(4 x \right)} \]chain algebra algebra simplifyApply the chain rule to the logarithm. Simplify the fraction by canceling the 4. Simplify the product of 1/x and x. Combine the remaining terms.✓ Proved
Answer \( \log{\left(4 x \right)} \)
✓ Nihil obstat 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. Reviewers found nothing wrong with the explanation.
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 |
| 7 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 log is undefined for non-positive arguments |
| 8 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 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 |
| 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: passqwen3.6:27b-mlx: pass — The solution correctly applies the product rule, linearity of differentiation, and the chain rule for the logarithmic term. Each step isolates a single logical transformation, and the labels accurately reflect the operations performed.
Every verdict on record (6)
qwen3.6:27b-mlx: pass 2026-09-21 — The solution correctly applies the product rule, linearity of differentiation, and the chain rule for the logarithmic term. Each step isolates a single logical transformation, and the labels accurately reflect the operations performed.gpt-oss:20b: pass 2026-09-21qwen3.6:27b-mlx: pass 2026-09-20 — The solution correctly applies the product rule, linearity of differentiation, and the chain rule for the logarithmic term. Each step isolates a single operation and uses labels from the allowed vocabulary.gpt-oss:20b: pass 2026-09-20qwen3.6:27b-mlx: pass 2026-09-20 — The solution correctly applies the product rule, linearity of the derivative, and the chain rule for the logarithm. Each step isolates a single transformation, and the labels accurately reflect the operations performed.gpt-oss:20b: pass 2026-09-20
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.