Derivative of \( \displaystyle 2 x \ln{\left(4 x + 2 \right)} - 2 x + \ln{\left(2 x + 1 \right)} \)
Problem 2.1925 · hard
Differentiate \( \displaystyle f(x) = 2 x \ln{\left(4 x + 2 \right)} - 2 x + \ln{\left(2 x + 1 \right)} \).
- \[ \frac{d}{d x} \left(2 x \ln{\left(4 x + 2 \right)} - 2 x + \ln{\left(2 x + 1 \right)}\right) \]derivativeStart with the derivative of the function.✓ Proved
- \[ = - \frac{d}{d x} 2 x + \frac{d}{d x} 2 x \ln{\left(4 x + 2 \right)} + \frac{d}{d x} \ln{\left(2 x + 1 \right)} \]sumApply the sum rule for derivatives.✓ Proved
- \[ = \frac{d}{d x} 2 x \ln{\left(4 x + 2 \right)} + \frac{d}{d x} \ln{\left(2 x + 1 \right)} - 2 \]constantDifferentiate the linear term -2*x.✓ Proved
- \[ = 2 x \frac{d}{d x} \ln{\left(4 x + 2 \right)} + \ln{\left(4 x + 2 \right)} \frac{d}{d x} 2 x + \frac{d}{d x} \ln{\left(2 x + 1 \right)} - 2 \]productApply the product rule to the first term.✓ Proved
- \[ = 2 x \frac{d}{d x} \ln{\left(4 x + 2 \right)} + 2 \ln{\left(4 x + 2 \right)} + \frac{d}{d x} \ln{\left(2 x + 1 \right)} - 2 \]constant-multipleDifferentiate the term 2*x.✓ Proved
- \[ = \frac{2 x \frac{d}{d x} \left(4 x + 2\right)}{4 x + 2} + 2 \ln{\left(4 x + 2 \right)} + \frac{d}{d x} \ln{\left(2 x + 1 \right)} - 2 \]chainApply the chain rule to the logarithm.✓ Proved
- \[ = \frac{8 x}{4 x + 2} + 2 \ln{\left(4 x + 2 \right)} + \frac{d}{d x} \ln{\left(2 x + 1 \right)} - 2 \]derivativeDifferentiate the inner function 4*x + 2.✓ Proved
- \[ = \frac{8 x}{4 x + 2} + 2 \ln{\left(4 x + 2 \right)} - 2 + \frac{\frac{d}{d x} \left(2 x + 1\right)}{2 x + 1} \]chainApply the chain rule to the second logarithm.✓ Proved
- \[ = \frac{8 x}{4 x + 2} + 2 \ln{\left(4 x + 2 \right)} - 2 + \frac{2}{2 x + 1} \]derivative algebraDifferentiate the inner function 2*x + 1. Multiply the terms in the numerator.✓ Proved
- \[ = \frac{4 x}{2 x + 1} + 2 \ln{\left(4 x + 2 \right)} - 2 + \frac{2}{2 x + 1} \]algebraSimplify the fraction (8*x)/(4*x + 2) by dividing by 2.✓ Proved
- \[ = 2 \ln{\left(4 x + 2 \right)} - 2 + \frac{4 x + 2}{2 x + 1} \]algebra algebraCombine the fractions with the same denominator. Factor the numerator 4*x + 2.✓ Proved
- \[ = 2 \ln{\left(4 x + 2 \right)} \]algebra simplifyCancel the common factor (2*x + 1). Final simplification.✓ Proved
Answer \( 2 \ln{\left(4 x + 2 \right)} \)
✓ 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
| 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 undefined where 4*x + 2 = 0 |
| 7 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 log is undefined for non-positive arguments undefined where 4*x + 2 = 0 |
| 8 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 log is undefined for non-positive arguments undefined where 4*x + 2 = 0 undefined where 2*x + 1 = 0 |
| 9 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 log is undefined for non-positive arguments undefined where 2*x + 1 = 0 undefined where 4*x + 2 = 0 |
| 10 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 log is undefined for non-positive arguments undefined where 2*x + 1 = 0 undefined where 4*x + 2 = 0 |
| 11 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 log is undefined for non-positive arguments undefined where 2*x + 1 = 0 undefined where 4*x + 2 = 0 |
| 12 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 log is undefined for non-positive arguments undefined where 2*x + 1 = 0 |
| 13 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 log is undefined for non-positive arguments undefined where 2*x + 1 = 0 |
| 14 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 log is undefined for non-positive arguments undefined where 2*x + 1 = 0 |
| 15 | ✓ 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. All labels are appropriate for the transformations performed.
Every verdict on record (4)
gpt-oss:20b: pass 2026-10-09qwen3.6:27b-mlx: pass 2026-10-09 — The solution correctly applies differentiation rules step-by-step, adhering to the one-change-per-step constraint. All labels are appropriate for the transformations performed.gpt-oss:20b: pass 2026-10-09qwen3.6:27b-mlx: pass 2026-10-09 — The solution correctly applies differentiation rules step-by-step, adhering to the one-change-per-step constraint. The algebraic simplifications are valid and clearly labeled.
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 2026-10-09 with SymPy 1.14.0.