∫Calc Practice

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 \( \displaystyle f(x) = 5 x \ln{\left(4 x + 2 \right)} - 5 x + \frac{5 \ln{\left(2 x + 1 \right)}}{2} \).
  1. \[ \frac{d}{d x} \left(5 x \ln{\left(4 x + 2 \right)} - 5 x + \frac{5 \ln{\left(2 x + 1 \right)}}{2}\right) \]
    sumStart with the derivative of the entire function.✓ Proved
  2. \[ = - \frac{d}{d x} 5 x + \frac{d}{d x} 5 x \ln{\left(4 x + 2 \right)} + \frac{d}{d x} \frac{5 \ln{\left(2 x + 1 \right)}}{2} \]
    sumApply the sum rule to separate the terms.✓ Proved
  3. \[ = \frac{d}{d x} 5 x \ln{\left(4 x + 2 \right)} + \frac{d}{d x} \frac{5 \ln{\left(2 x + 1 \right)}}{2} - 5 \]
    constantThe derivative of 5*x is 5.✓ Proved
  4. \[ = 5 \frac{d}{d x} x \ln{\left(4 x + 2 \right)} + \frac{d}{d x} \frac{5 \ln{\left(2 x + 1 \right)}}{2} - 5 \]
    constant-multipleFactor out the constant 5 from the first term.✓ Proved
  5. \[ = 5 x \frac{d}{d x} \ln{\left(4 x + 2 \right)} + 5 \ln{\left(4 x + 2 \right)} \frac{d}{d x} x + \frac{d}{d x} \frac{5 \ln{\left(2 x + 1 \right)}}{2} - 5 \]
    productApply the product rule to the first term.✓ Proved
  6. \[ = 5 x \frac{d}{d x} \ln{\left(4 x + 2 \right)} + 5 \ln{\left(4 x + 2 \right)} + \frac{d}{d x} \frac{5 \ln{\left(2 x + 1 \right)}}{2} - 5 \]
    derivativeThe derivative of x is 1.✓ Proved
  7. \[ = 5 x \frac{d}{d x} \ln{\left(4 x + 2 \right)} + 5 \ln{\left(4 x + 2 \right)} + \frac{5 \frac{d}{d x} \ln{\left(2 x + 1 \right)}}{2} - 5 \]
    constant-multipleFactor out 5/2 from the third term.✓ Proved
  8. \[ = \frac{20 x}{4 x + 2} + 5 \ln{\left(4 x + 2 \right)} - 5 + \frac{5}{2 x + 1} \]
    chain algebra algebraApply the chain rule to the logarithmic terms. Simplify the fractions. Distribute the 5 and simplify the terms.✓ Proved
  9. \[ = \frac{10 x}{2 x + 1} + 5 \ln{\left(4 x + 2 \right)} - 5 + \frac{5}{2 x + 1} \]
    algebraSimplify the fraction (20*x)/(4*x + 2) by dividing numerator and denominator by 2.✓ Proved
  10. \[ = 5 \ln{\left(4 x + 2 \right)} - 5 + \frac{10 x + 5}{2 x + 1} \]
    algebra algebraCombine the fractions with the same denominator. Factor out 5 from the numerator.✓ Proved
  11. \[ = 5 \ln{\left(4 x + 2 \right)} \]
    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
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
undefined where 4*x + 2 = 0
undefined where 2*x + 1 = 0
9✓ Provedsympy 1.14.0simplify(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✓ Provedsympy 1.14.0simplify(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✓ Provedsympy 1.14.0simplify(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✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
log is undefined for non-positive arguments
undefined where 2*x + 1 = 0
13✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
log is undefined for non-positive arguments
undefined where 2*x + 1 = 0
14✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
log is undefined for non-positive arguments
undefined where 2*x + 1 = 0
15✓ 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: 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 2026-10-13
  • qwen3.6:27b-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.