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Derivative of \( \displaystyle 3 x \ln{\left(x + 2 \right)} - 3 x + 6 \ln{\left(x + 2 \right)} \)

Problem 2.296 · hard Beautiful

Differentiate \( \displaystyle f(x) = 3 x \ln{\left(x + 2 \right)} - 3 x + 6 \ln{\left(x + 2 \right)} \).
  1. \[ \frac{d}{d x} \left(3 x \ln{\left(x + 2 \right)} - 3 x + 6 \ln{\left(x + 2 \right)}\right) \]
    derivativeStart with the derivative of the function.✓ Proved
  2. \[ = - \frac{d}{d x} 3 x + \frac{d}{d x} 3 x \ln{\left(x + 2 \right)} + \frac{d}{d x} 6 \ln{\left(x + 2 \right)} \]
    sumApply the sum rule.✓ Proved
  3. \[ = \frac{d}{d x} 3 x \ln{\left(x + 2 \right)} + \frac{d}{d x} 6 \ln{\left(x + 2 \right)} - 3 \]
    constantDifferentiate the linear term.✓ Proved
  4. \[ = 3 x \frac{d}{d x} \ln{\left(x + 2 \right)} + 3 \ln{\left(x + 2 \right)} + \frac{d}{d x} 6 \ln{\left(x + 2 \right)} - 3 \]
    productApply the product rule to the first term.✓ Proved
  5. \[ = \frac{3 x}{x + 2} + 3 \ln{\left(x + 2 \right)} - 3 + \frac{6}{x + 2} \]
    logarithmic algebraDifferentiate the logarithmic terms. Simplify the fractions.✓ Proved
  6. \[ = 3 \ln{\left(x + 2 \right)} - 3 + \frac{3 x + 6}{x + 2} \]
    algebra algebraCombine the fractions with the same denominator. Factor the numerator of the fraction.✓ Proved
  7. \[ = 3 \ln{\left(x + 2 \right)} \]
    algebra simplifySimplify the fraction. Final simplification.✓ Proved
Answer \( 3 \log{\left(x + 2 \right)} \)

✓ 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
undefined where x + 2 = 0
6✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
log is undefined for non-positive arguments
undefined where x + 2 = 0
7✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
log is undefined for non-positive arguments
undefined where x + 2 = 0
8✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
log is undefined for non-positive arguments
undefined where x + 2 = 0
9✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
log is undefined for non-positive arguments
undefined where x + 2 = 0
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 differentiation rules step-by-step, adhering to the one-change-per-step constraint. All labels are valid and accurately describe the operations performed.
Every verdict on record (12)
  • 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 valid and accurately describe the operations performed.
  • 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
  • deepseek-r1:70b: pass 2026-09-19
  • gpt-oss:20b: pass 2026-09-19
  • qwen3.6:27b-mlx: pass 2026-09-19
  • deepseek-r1:70b: pass 2026-09-19
  • gpt-oss:20b: pass 2026-09-19
  • gpt-oss:20b: fail 2026-09-17 — Step 3 incorrectly labels the rule as "constant"; differentiating 3*x requires the linear (power) rule, not a constant rule.
  • 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.