Derivative of \( \displaystyle 5 x \ln{\left(4 x + 2 \right)} - 5 x + \frac{5 \ln{\left(2 x + 1 \right)}}{2} \)
Problem 2.2186 · hard
Differentiate \( \displaystyle f(x) = 5 x \ln{\left(4 x + 2 \right)} - 5 x + \frac{5 \ln{\left(2 x + 1 \right)}}{2} \).
- \[ \frac{d}{d x} \left(5 x \ln{\left(4 x + 2 \right)} - 5 x + \frac{5 \ln{\left(2 x + 1 \right)}}{2}\right) \]sumStart with the derivative of the entire function.✓ Proved
- \[ = - \frac{d}{d x} 5 x + \frac{d}{d x} 5 x \ln{\left(4 x + 2 \right)} + \frac{d}{d x} \frac{5 \ln{\left(2 x + 1 \right)}}{2} \]sumApply the sum rule to separate the terms.✓ Proved
- \[ = \frac{d}{d x} 5 x \ln{\left(4 x + 2 \right)} + \frac{d}{d x} \frac{5 \ln{\left(2 x + 1 \right)}}{2} - 5 \]constantThe derivative of 5*x is 5.✓ Proved
- \[ = 5 \frac{d}{d x} x \ln{\left(4 x + 2 \right)} + \frac{d}{d x} \frac{5 \ln{\left(2 x + 1 \right)}}{2} - 5 \]constant-multipleFactor out the constant 5 from the first term.✓ Proved
- \[ = 5 x \frac{d}{d x} \ln{\left(4 x + 2 \right)} + 5 \ln{\left(4 x + 2 \right)} \frac{d}{d x} x + \frac{d}{d x} \frac{5 \ln{\left(2 x + 1 \right)}}{2} - 5 \]productApply the product rule to the first term.✓ Proved
- \[ = 5 x \frac{d}{d x} \ln{\left(4 x + 2 \right)} + 5 \ln{\left(4 x + 2 \right)} + \frac{d}{d x} \frac{5 \ln{\left(2 x + 1 \right)}}{2} - 5 \]derivativeThe derivative of x is 1.✓ Proved
- \[ = 5 x \frac{d}{d x} \ln{\left(4 x + 2 \right)} + 5 \ln{\left(4 x + 2 \right)} + \frac{5 \frac{d}{d x} \ln{\left(2 x + 1 \right)}}{2} - 5 \]constant-multipleFactor out 5/2 from the third term.✓ Proved
- \[ = \frac{20 x}{4 x + 2} + 5 \ln{\left(4 x + 2 \right)} - 5 + \frac{5}{2 x + 1} \]chain algebra algebraApply the chain rule to the logarithmic terms. Simplify the fractions. Distribute the 5 and simplify the terms.✓ Proved
- \[ = \frac{10 x}{2 x + 1} + 5 \ln{\left(4 x + 2 \right)} - 5 + \frac{5}{2 x + 1} \]algebraSimplify the fraction (20*x)/(4*x + 2) by dividing numerator and denominator by 2.✓ Proved
- \[ = 5 \ln{\left(4 x + 2 \right)} - 5 + \frac{10 x + 5}{2 x + 1} \]algebra algebraCombine the fractions with the same denominator. Factor out 5 from the numerator.✓ Proved
- \[ = 5 \ln{\left(4 x + 2 \right)} \]algebra simplifySimplify the fraction (2*x + 1)/(2*x + 1) to 1. Final simplification.✓ Proved
Answer \( 5 \ln{\left(4 x + 2 \right)} \)
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. The reviewers disagree about how one step is explained; every verdict is in the receipt.
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 + 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 4*x + 2 = 0 undefined where 2*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 + 2 = 0 undefined where 2*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 + 2 = 0 undefined where 2*x + 1 = 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: fail (error) — Step 8 applies the chain rule to two logarithmic terms in a single line, violating the rule that each step must change only one thing. This combines two separate derivative applications into one step, which is not allowed.qwen3.6:27b-mlx: pass — The solution correctly applies differentiation rules and algebraic simplifications. Each step isolates a single operation, and the labels accurately reflect the rules applied.
Every verdict on record (4)
gpt-oss:20b: fail (error) 2026-10-13 — Step 8 applies the chain rule to two logarithmic terms in a single line, violating the rule that each step must change only one thing. This combines two separate derivative applications into one step, which is not allowed.qwen3.6:27b-mlx: pass 2026-10-13 — The solution correctly applies differentiation rules and algebraic simplifications. Each step isolates a single operation, and the labels accurately reflect the rules applied.gpt-oss:20b: pass 2026-10-13qwen3.6:27b-mlx: pass 2026-10-13 — 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 2026-10-13 with SymPy 1.14.0.