Derivative of \( \displaystyle - 3 x + \left(3 x - \frac{3}{4}\right) \ln{\left(4 x - 1 \right)} \)
Problem 2.1661 · hard
Differentiate \( \displaystyle f(x) = - 3 x + \left(3 x - \frac{3}{4}\right) \ln{\left(4 x - 1 \right)} \).
- \[ \frac{d}{d x} \left(- 3 x + \left(3 x - \frac{3}{4}\right) \ln{\left(4 x - 1 \right)}\right) \]derivativeStart with the derivative of the function.✓ Proved
- \[ = \frac{d}{d x} \left(- 3 x\right) + \frac{d}{d x} \left(3 x - \frac{3}{4}\right) \ln{\left(4 x - 1 \right)} \]sumApply the sum rule.✓ Proved
- \[ = \left(3 x - \frac{3}{4}\right) \frac{d}{d x} \ln{\left(4 x - 1 \right)} + \ln{\left(4 x - 1 \right)} \frac{d}{d x} \left(3 x - \frac{3}{4}\right) + \frac{d}{d x} \left(- 3 x\right) \]productApply the product rule to the second term.✓ Proved
- \[ = \left(3 x - \frac{3}{4}\right) \frac{d}{d x} \ln{\left(4 x - 1 \right)} + \left(- \frac{d}{d x} \frac{3}{4} + \frac{d}{d x} 3 x\right) \ln{\left(4 x - 1 \right)} + \frac{d}{d x} \left(- 3 x\right) \]algebraDistribute the derivative over the subtraction.✓ Proved
- \[ = \left(3 x - \frac{3}{4}\right) \frac{d}{d x} \ln{\left(4 x - 1 \right)} - \ln{\left(4 x - 1 \right)} \frac{d}{d x} \frac{3}{4} + \ln{\left(4 x - 1 \right)} \frac{d}{d x} 3 x + \frac{d}{d x} \left(- 3 x\right) \]algebraExpand the expression.✓ Proved
- \[ = \left(3 x - \frac{3}{4}\right) \frac{d}{d x} \ln{\left(4 x - 1 \right)} + \ln{\left(4 x - 1 \right)} \frac{d}{d x} 3 x + \frac{d}{d x} \left(- 3 x\right) \]constantThe derivative of the constant 3/4 is zero.✓ Proved
- \[ = \left(3 x - \frac{3}{4}\right) \frac{d}{d x} \ln{\left(4 x - 1 \right)} + 3 \ln{\left(4 x - 1 \right)} + \frac{d}{d x} \left(- 3 x\right) \]constant-multipleDifferentiate 3*x.✓ Proved
- \[ = \frac{\left(3 x - \frac{3}{4}\right) \frac{d}{d x} \left(4 x - 1\right)}{4 x - 1} + 3 \ln{\left(4 x - 1 \right)} + \frac{d}{d x} \left(- 3 x\right) \]chainApply the chain rule to the logarithm.✓ Proved
- \[ = \frac{4 \left(3 x - \frac{3}{4}\right)}{4 x - 1} + 3 \ln{\left(4 x - 1 \right)} + \frac{d}{d x} \left(- 3 x\right) \]derivativeDifferentiate the inner function 4*x - 1.✓ Proved
- \[ = 3 \ln{\left(4 x - 1 \right)} + \frac{d}{d x} \left(- 3 x\right) + \frac{12 x - 3}{4 x - 1} \]algebraMultiply the terms in the last part.✓ Proved
- \[ = 3 \ln{\left(4 x - 1 \right)} - 3 + \frac{12 x - 3}{4 x - 1} \]derivative algebraDifferentiate the first term. Factor out 3 from the numerator.✓ Proved
- \[ = 3 \ln{\left(4 x - 1 \right)} \]simplify simplifyCancel the common factor (4*x - 1). Combine the constant terms.✓ Proved
Answer \( 3 \ln{\left(4 x - 1 \right)} \)
✓ 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 undefined where 4*x - 1 = 0 |
| 9 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 log is undefined for non-positive arguments undefined where 4*x - 1 = 0 |
| 10 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 log is undefined for non-positive arguments undefined where 4*x - 1 = 0 |
| 11 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 log is undefined for non-positive arguments undefined where 4*x - 1 = 0 |
| 12 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 log is undefined for non-positive arguments undefined where 4*x - 1 = 0 |
| 13 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 log is undefined for non-positive arguments undefined where 4*x - 1 = 0 |
| 14 | ✓ 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 differentiation rules step-by-step, adhering to the one-change-per-step constraint. The algebraic simplifications and rule applications are valid and clearly labeled.
Every verdict on record (4)
gpt-oss:20b: pass 2026-10-06qwen3.6:27b-mlx: pass 2026-10-06 — The solution correctly applies differentiation rules step-by-step, adhering to the one-change-per-step constraint. The algebraic simplifications and rule applications are valid and clearly labeled.qwen3.6:27b-mlx: pass 2026-10-06gpt-oss:20b: pass 2026-10-06
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 2026-10-06 with SymPy 1.14.0.