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 \( \displaystyle f(x) = - \frac{x^{2}}{4} - x + \left(\frac{x^{2}}{2} + 2 x + 2\right) \ln{\left(x + 2 \right)} \).
- \[ \frac{d}{d x} \left(- \frac{x^{2}}{4} - x + \left(\frac{x^{2}}{2} + 2 x + 2\right) \ln{\left(x + 2 \right)}\right) \]sumStart with the derivative of the entire function.✓ Proved
- \[ = \frac{d}{d x} \left(- x\right) + \frac{d}{d x} \left(- \frac{x^{2}}{4}\right) + \frac{d}{d x} \left(\frac{x^{2}}{2} + 2 x + 2\right) \ln{\left(x + 2 \right)} \]sumSplit the derivative into parts using the sum rule.✓ Proved
- \[ = \left(\frac{x^{2}}{2} + 2 x + 2\right) \frac{d}{d x} \ln{\left(x + 2 \right)} + \ln{\left(x + 2 \right)} \frac{d}{d x} \left(\frac{x^{2}}{2} + 2 x + 2\right) + \frac{d}{d x} \left(- x\right) + \frac{d}{d x} \left(- \frac{x^{2}}{4}\right) \]productApply the product rule to the third term.✓ Proved
- \[ = \left(x + 2\right) \ln{\left(x + 2 \right)} + \left(\frac{x^{2}}{2} + 2 x + 2\right) \frac{d}{d x} \ln{\left(x + 2 \right)} + \frac{d}{d x} \left(- x\right) + \frac{d}{d x} \left(- \frac{x^{2}}{4}\right) \]derivativeDifferentiate the polynomial part of the product.✓ Proved
- \[ = \left(x + 2\right) \ln{\left(x + 2 \right)} + \frac{d}{d x} \left(- x\right) + \frac{d}{d x} \left(- \frac{x^{2}}{4}\right) + \frac{\frac{x^{2}}{2} + 2 x + 2}{x + 2} \]derivativeDifferentiate the logarithmic part using the chain rule.✓ Proved
- \[ = - \frac{x}{2} + \left(x + 2\right) \ln{\left(x + 2 \right)} - 1 + \frac{\frac{x^{2}}{2} + 2 x + 2}{x + 2} \]derivativeDifferentiate the remaining simple terms.✓ Proved
- \[ = - \frac{x}{2} + \left(x + 2\right) \ln{\left(x + 2 \right)} - 1 + \frac{0.5 x^{2} + 2 x + 2}{x + 2} \]algebraConvert coefficients to decimals for consistency.✓ Proved
- \[ = \left(x + 2\right) \ln{\left(x + 2 \right)} \]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
| 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 undefined where x + 2 = 0 |
| 6 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 log is undefined for non-positive arguments undefined where x + 2 = 0 |
| 7 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 log is undefined for non-positive arguments undefined where x + 2 = 0 |
| 8 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 log is undefined for non-positive arguments undefined where x + 2 = 0 |
| 9 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 log is undefined for non-positive arguments |
| 10 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 log is undefined for non-positive arguments |
| 11 | ✓ 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 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 2026-10-09qwen3.6:27b-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 2026-10-09qwen3.6:27b-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.