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

Problem 2.1922 · hard

Differentiate \( \displaystyle f(x) = - \frac{x^{2}}{4} - x + \left(\frac{x^{2}}{2} + 2 x + 2\right) \ln{\left(x + 2 \right)} \).
  1. \[ \frac{d}{d x} \left(- \frac{x^{2}}{4} - x + \left(\frac{x^{2}}{2} + 2 x + 2\right) \ln{\left(x + 2 \right)}\right) \]
    sumStart with the derivative of the entire function.✓ Proved
  2. \[ = \frac{d}{d x} \left(- x\right) + \frac{d}{d x} \left(- \frac{x^{2}}{4}\right) + \frac{d}{d x} \left(\frac{x^{2}}{2} + 2 x + 2\right) \ln{\left(x + 2 \right)} \]
    sumSplit the derivative into parts using the sum rule.✓ Proved
  3. \[ = \left(\frac{x^{2}}{2} + 2 x + 2\right) \frac{d}{d x} \ln{\left(x + 2 \right)} + \ln{\left(x + 2 \right)} \frac{d}{d x} \left(\frac{x^{2}}{2} + 2 x + 2\right) + \frac{d}{d x} \left(- x\right) + \frac{d}{d x} \left(- \frac{x^{2}}{4}\right) \]
    productApply the product rule to the third term.✓ Proved
  4. \[ = \left(x + 2\right) \ln{\left(x + 2 \right)} + \left(\frac{x^{2}}{2} + 2 x + 2\right) \frac{d}{d x} \ln{\left(x + 2 \right)} + \frac{d}{d x} \left(- x\right) + \frac{d}{d x} \left(- \frac{x^{2}}{4}\right) \]
    derivativeDifferentiate the polynomial part of the product.✓ Proved
  5. \[ = \left(x + 2\right) \ln{\left(x + 2 \right)} + \frac{d}{d x} \left(- x\right) + \frac{d}{d x} \left(- \frac{x^{2}}{4}\right) + \frac{\frac{x^{2}}{2} + 2 x + 2}{x + 2} \]
    derivativeDifferentiate the logarithmic part using the chain rule.✓ Proved
  6. \[ = - \frac{x}{2} + \left(x + 2\right) \ln{\left(x + 2 \right)} - 1 + \frac{\frac{x^{2}}{2} + 2 x + 2}{x + 2} \]
    derivativeDifferentiate the remaining simple terms.✓ Proved
  7. \[ = - \frac{x}{2} + \left(x + 2\right) \ln{\left(x + 2 \right)} - 1 + \frac{0.5 x^{2} + 2 x + 2}{x + 2} \]
    algebraConvert coefficients to decimals for consistency.✓ Proved
  8. \[ = \left(x + 2\right) \ln{\left(x + 2 \right)} \]
    algebra algebra algebra simplifyFactor the quadratic expression in the numerator. Simplify the fraction by canceling (x + 2). Distribute the constant. Combine all remaining terms.✓ Proved
Answer \( \left(x + 2\right) \ln{\left(x + 2 \right)} \)

✓ 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
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
undefined where x + 2 = 0
6✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
log is undefined for non-positive arguments
undefined where x + 2 = 0
7✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
log is undefined for non-positive arguments
undefined where x + 2 = 0
8✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
log is undefined for non-positive arguments
undefined where x + 2 = 0
9✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
log is undefined for non-positive arguments
10✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
log is undefined for non-positive arguments
11✓ 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: pass
  • qwen3.6:27b-mlx: pass — The solution correctly applies differentiation rules and algebraic simplifications. Each step adheres to the single-change constraint and uses valid labels from the fixed vocabulary.
Every verdict on record (4)
  • gpt-oss:20b: pass 2026-10-09
  • qwen3.6:27b-mlx: pass 2026-10-09 — The solution correctly applies differentiation rules and algebraic simplifications. Each step adheres to the single-change constraint and uses valid labels from the fixed vocabulary.
  • gpt-oss:20b: pass 2026-10-09
  • qwen3.6:27b-mlx: fail (style) 2026-10-09 — Step 5 is labeled 'derivative' but the note explicitly states 'using the chain rule'; since 'chain' is in the vocabulary, the label should be 'chain' to accurately reflect the rule applied. Additionally, Step 7 introduces decimal coefficients unnecessarily, which is a stylistic inconsistency with the previous exact fractional forms.

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.