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Derivative of \( \displaystyle x \left(\ln{\left(5 x \right)} - 1\right) \)

Problem 2.162 · hard

Differentiate \( \displaystyle f(x) = x \left(\ln{\left(5 x \right)} - 1\right) \).
  1. \[ \frac{d}{d x} x \left(\ln{\left(5 x \right)} - 1\right) \]
    derivativeStart with the derivative of the function.✓ Proved
  2. \[ = x \frac{d}{d x} \left(\ln{\left(5 x \right)} - 1\right) + \left(\ln{\left(5 x \right)} - 1\right) \frac{d}{d x} x \]
    productApply the product rule.✓ Proved
  3. \[ = x \frac{d}{d x} \left(\ln{\left(5 x \right)} - 1\right) + \ln{\left(5 x \right)} - 1 \]
    derivativeDifferentiate the first part of the product.✓ Proved
  4. \[ = x \left(- \frac{d}{d x} 1 + \frac{d}{d x} \ln{\left(5 x \right)}\right) + \ln{\left(5 x \right)} - 1 \]
    sumDistribute the derivative over the subtraction.✓ Proved
  5. \[ = x \frac{d}{d x} \ln{\left(5 x \right)} + \ln{\left(5 x \right)} - 1 \]
    constant algebraThe derivative of a constant is zero. Simplify the expression.✓ Proved
  6. \[ = \ln{\left(5 x \right)} \]
    chain algebra algebra simplifyApply the chain rule to the logarithm. Simplify the fraction. Multiply x by 1/x. Combine the constant terms.✓ Proved
Answer \( \log{\left(5 x \right)} \)

✓ 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
LineStatusChecked byDetail
1✓ Provedsympy 1.14.0line 1 is the problem as stated
2✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
log is undefined for non-positive arguments
3✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
log is undefined for non-positive arguments
4✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
log is undefined for non-positive arguments
5✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
log is undefined for non-positive arguments
6✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
log is undefined for non-positive arguments
7✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
log is undefined for non-positive arguments
8✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
log is undefined for non-positive arguments
9✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
log is undefined for non-positive arguments
10✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
log is undefined for non-positive arguments
answer✓ Provedsympy 1.14.0final line against the stated answer: simplify(a - b) reduced to 0
log is undefined for non-positive arguments
answer, a second way✓ Provedsympy 1.14.0SymPy differentiated f directly and got the stated answer

Reviewers

  • gpt-oss:20b: pass
  • deepseek-r1:70b: pass
  • qwen3.6:27b-mlx: pass — The solution correctly applies the product rule, sum rule, chain rule, and algebraic simplifications in a logical sequence. Each step changes only one aspect of the expression and uses an appropriate label from the fixed vocabulary.
Every verdict on record (15)
  • qwen3.6:27b-mlx: pass 2026-09-20 — The solution correctly applies the product rule, sum rule, chain rule, and algebraic simplifications in a logical sequence. Each step changes only one aspect of the expression and uses an appropriate label from the fixed vocabulary.
  • gpt-oss:20b: pass 2026-09-20
  • qwen3.6:27b-mlx: pass 2026-09-20
  • gpt-oss:20b: pass 2026-09-20
  • qwen3.6:27b-mlx: pass 2026-09-19 — The solution correctly applies the product rule, linearity of differentiation, and the chain rule. Each step modifies only one aspect of the expression and uses valid labels from the fixed vocabulary.
  • deepseek-r1:70b: pass 2026-09-19
  • gpt-oss:20b: pass 2026-09-19
  • qwen3.6:27b-mlx: pass 2026-09-19 — The solution correctly applies the product rule, chain rule, and simplification steps. Each step changes only one aspect of the expression and uses valid labels from the fixed vocabulary.
  • deepseek-r1:70b: pass 2026-09-19
  • gpt-oss:20b: pass 2026-09-19
  • qwen3.6:27b-mlx: pass 2026-09-18
  • deepseek-r1:70b: pass 2026-09-18
  • gpt-oss:20b: pass 2026-09-18
  • gpt-oss:20b: pass 2026-09-17
  • deepseek-r1:70b: pass 2026-09-17

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.