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Derivative of \( \displaystyle x \ln{\left(4 x - 3 \right)} - x - \frac{3 \ln{\left(4 x - 3 \right)}}{4} \)

Problem 2.205 · hard Beautiful

Differentiate \( \displaystyle f(x) = x \ln{\left(4 x - 3 \right)} - x - \frac{3 \ln{\left(4 x - 3 \right)}}{4} \).
  1. \[ \frac{d}{d x} \left(x \ln{\left(4 x - 3 \right)} - x - \frac{3 \ln{\left(4 x - 3 \right)}}{4}\right) \]
    derivativeStart with the derivative of the function.✓ Proved
  2. \[ = - \frac{d}{d x} x + \frac{d}{d x} x \ln{\left(4 x - 3 \right)} - \frac{d}{d x} \frac{3 \ln{\left(4 x - 3 \right)}}{4} \]
    sumApply the sum rule for derivatives.✓ Proved
  3. \[ = \frac{d}{d x} x \ln{\left(4 x - 3 \right)} - \frac{d}{d x} \frac{3 \ln{\left(4 x - 3 \right)}}{4} - 1 \]
    constantThe derivative of x is 1.✓ Proved
  4. \[ = \frac{d}{d x} x \ln{\left(4 x - 3 \right)} - \frac{3 \frac{d}{d x} \ln{\left(4 x - 3 \right)}}{4} - 1 \]
    constant-multiplePull out the constant factor 3/4.✓ Proved
  5. \[ = x \frac{d}{d x} \ln{\left(4 x - 3 \right)} + \ln{\left(4 x - 3 \right)} \frac{d}{d x} x - \frac{3 \frac{d}{d x} \ln{\left(4 x - 3 \right)}}{4} - 1 \]
    productApply the product rule to the first term.✓ Proved
  6. \[ = x \frac{d}{d x} \ln{\left(4 x - 3 \right)} + \ln{\left(4 x - 3 \right)} - \frac{3 \frac{d}{d x} \ln{\left(4 x - 3 \right)}}{4} - 1 \]
    derivative algebraThe derivative of x is 1. Rearrange the terms.✓ Proved
  7. \[ = \left(x - \frac{3}{4}\right) \frac{d}{d x} \ln{\left(4 x - 3 \right)} + \ln{\left(4 x - 3 \right)} - 1 \]
    algebraGroup the terms containing the derivative.✓ Proved
  8. \[ = \frac{\left(x - \frac{3}{4}\right) \frac{d}{d x} \left(4 x - 3\right)}{4 x - 3} + \ln{\left(4 x - 3 \right)} - 1 \]
    chainApply the chain rule to the logarithm.✓ Proved
  9. \[ = \ln{\left(4 x - 3 \right)} \]
    derivative algebra algebra simplifyThe derivative of 4*x - 3 is 4. Distribute the 4 in the numerator. Simplify the fraction. Final simplification.✓ Proved
Answer \( \log{\left(4 x - 3 \right)} \)

✓ 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
undefined where 4*x - 3 = 0
10✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
log is undefined for non-positive arguments
undefined where 4*x - 3 = 0
11✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
log is undefined for non-positive arguments
12✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
log is undefined for non-positive arguments
13✓ 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 and using valid labels from the fixed vocabulary.
Every verdict on record (15)
  • 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 and using valid labels 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 differentiation rules step-by-step, adhering to the one-change-per-step constraint. All labels are appropriate and the logic is sound.
  • 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
  • qwen3.6:27b-mlx: pass 2026-09-18 — The solution correctly applies differentiation rules step-by-step, adhering to the one-change-per-step constraint and using valid labels from the fixed vocabulary.
  • deepseek-r1:70b: pass 2026-09-18
  • gpt-oss:20b: pass 2026-09-18
  • gpt-oss:20b: fail 2026-09-17 — Step 3 incorrectly labels the rule as "constant"; differentiating x is not a constant rule, so the rule label is misleading.
  • 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.