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Derivative of \( \displaystyle \frac{5 x^{2}}{4} + x - \left(\frac{5 x^{2}}{2} + 2 x + \frac{2}{5}\right) \ln{\left(5 x + 2 \right)} \)

Problem 2.2127 · hard

Differentiate \( \displaystyle f(x) = \frac{5 x^{2}}{4} + x - \left(\frac{5 x^{2}}{2} + 2 x + \frac{2}{5}\right) \ln{\left(5 x + 2 \right)} \).
  1. \[ \frac{d}{d x} \left(\frac{5 x^{2}}{4} + x - \left(\frac{5 x^{2}}{2} + 2 x + \frac{2}{5}\right) \ln{\left(5 x + 2 \right)}\right) \]
    Start with the derivative of the function.✓ Proved
  2. \[ = \frac{d}{d x} x + \frac{d}{d x} \frac{5 x^{2}}{4} - \frac{d}{d x} \left(\frac{5 x^{2}}{2} + 2 x + \frac{2}{5}\right) \ln{\left(5 x + 2 \right)} \]
    sumApply the sum rule.✓ Proved
  3. \[ = - \left(\frac{5 x^{2}}{2} + 2 x + \frac{2}{5}\right) \frac{d}{d x} \ln{\left(5 x + 2 \right)} - \ln{\left(5 x + 2 \right)} \frac{d}{d x} \left(\frac{5 x^{2}}{2} + 2 x + \frac{2}{5}\right) + \frac{d}{d x} x + \frac{d}{d x} \frac{5 x^{2}}{4} \]
    productApply the product rule to the third term.✓ Proved
  4. \[ = - \left(\frac{5 x^{2}}{2} + 2 x + \frac{2}{5}\right) \frac{d}{d x} \ln{\left(5 x + 2 \right)} - \left(\frac{d}{d x} \frac{2}{5} + \frac{d}{d x} 2 x + \frac{d}{d x} \frac{5 x^{2}}{2}\right) \ln{\left(5 x + 2 \right)} + \frac{d}{d x} x + \frac{d}{d x} \frac{5 x^{2}}{4} \]
    sumApply the sum rule to the first part of the product rule.✓ Proved
  5. \[ = - \left(\frac{d}{d x} 2 x + \frac{d}{d x} \frac{5 x^{2}}{2}\right) \ln{\left(5 x + 2 \right)} - \left(\frac{5 x^{2}}{2} + 2 x + \frac{2}{5}\right) \frac{d}{d x} \ln{\left(5 x + 2 \right)} + \frac{d}{d x} x + \frac{d}{d x} \frac{5 x^{2}}{4} \]
    constant sumThe derivative of the constant 2/5 is 0. Apply the sum rule to the inner terms.✓ Proved
  6. \[ = - \left(5 x + 2\right) \ln{\left(5 x + 2 \right)} - \left(\frac{5 x^{2}}{2} + 2 x + \frac{2}{5}\right) \frac{d}{d x} \ln{\left(5 x + 2 \right)} + \frac{d}{d x} \frac{5 x^{2}}{4} + 1 \]
    derivativeDifferentiate the simple terms.✓ Proved
  7. \[ = - \left(5 x + 2\right) \ln{\left(5 x + 2 \right)} + \frac{d}{d x} \frac{5 x^{2}}{4} + 1 - \frac{5 \left(\frac{5 x^{2}}{2} + 2 x + \frac{2}{5}\right)}{5 x + 2} \]
    chain algebraApply the chain rule to the log term. Simplify the derivative of the log term.✓ Proved
  8. \[ = \frac{5 x}{2} - \left(5 x + 2\right) \ln{\left(5 x + 2 \right)} + 1 - \frac{5 \left(\frac{5 x^{2}}{2} + 2 x + \frac{2}{5}\right)}{5 x + 2} \]
    derivativeDifferentiate the first term.✓ Proved
  9. \[ = \frac{5 x}{2} - \left(5 x + 2\right) \ln{\left(5 x + 2 \right)} + 1 - \frac{\frac{25 x^{2}}{2} + 10 x + 2}{5 x + 2} \]
    algebraDistribute the 5 in the last term.✓ Proved
  10. \[ = \frac{5 x}{2} - \left(5 x + 2\right) \ln{\left(5 x + 2 \right)} + 1 - \frac{25 x^{2} + 20 x + 4}{10 x + 4} \]
    algebra algebra simplifySimplify the fraction. Expand the denominator. Final simplification of the expression.✓ Proved
Answer \( \left(- 5 x - 2\right) \ln{\left(5 x + 2 \right)} \)

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 5*x + 2 = 0
9✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
log is undefined for non-positive arguments
undefined where 5*x + 2 = 0
10✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
log is undefined for non-positive arguments
undefined where 5*x + 2 = 0
11✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
log is undefined for non-positive arguments
undefined where 5*x + 2 = 0
12✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
log is undefined for non-positive arguments
undefined where 5*x + 2 = 0
undefined where 10*x + 4 = 0
13✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
log is undefined for non-positive arguments
undefined where 10*x + 4 = 0
14✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
log is undefined for non-positive arguments
undefined where 10*x + 4 = 0
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
  • qwen3.6:27b-mlx: pass
Every verdict on record (4)
  • gpt-oss:20b: pass 2026-10-12
  • qwen3.6:27b-mlx: pass 2026-10-12
  • gpt-oss:20b: fail (error) 2026-10-12 — Step 7 incorrectly replaces the derivative of 2*x with 1, changing two terms in one step and producing an incorrect result.
  • qwen3.6:27b-mlx: fail (error) 2026-10-12 — The final answer provided in the task description is (-5*x - 2)*log(5*x + 2), but the solution steps derive 5*x/2 + 1 - (5*x + 2)*log(5*x + 2). The solution fails to simplify the rational term (25*x**2 + 20*x + 4)/(2*(5*x + 2)) to (5*x + 2)/2, which would cancel with the 5*x/2 + 1 terms to yield the stated answer. Thus, the steps do not lead to the stated answer.

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 2026-10-12 with SymPy 1.14.0.