Derivative of \( \displaystyle - \frac{x^{2}}{4} + \frac{3 x}{2} + \left(\frac{x^{2}}{2} - 3 x + \frac{9}{2}\right) \ln{\left(x - 3 \right)} \)
Problem 2.1577 · hard
Differentiate \( \displaystyle f(x) = - \frac{x^{2}}{4} + \frac{3 x}{2} + \left(\frac{x^{2}}{2} - 3 x + \frac{9}{2}\right) \ln{\left(x - 3 \right)} \).
- \[ \frac{d}{d x} \left(- \frac{x^{2}}{4} + \frac{3 x}{2} + \left(\frac{x^{2}}{2} - 3 x + \frac{9}{2}\right) \ln{\left(x - 3 \right)}\right) \]Start with the derivative of the function.✓ Proved
- \[ = \frac{d}{d x} \frac{3 x}{2} + \frac{d}{d x} \left(- \frac{x^{2}}{4}\right) + \frac{d}{d x} \left(\frac{x^{2}}{2} - 3 x + \frac{9}{2}\right) \ln{\left(x - 3 \right)} \]sumApply the sum rule.✓ Proved
- \[ = \left(\frac{x^{2}}{2} - 3 x + \frac{9}{2}\right) \frac{d}{d x} \ln{\left(x - 3 \right)} + \ln{\left(x - 3 \right)} \frac{d}{d x} \left(\frac{x^{2}}{2} - 3 x + \frac{9}{2}\right) + \frac{d}{d x} \frac{3 x}{2} + \frac{d}{d x} \left(- \frac{x^{2}}{4}\right) \]productApply the product rule to the third term.✓ Proved
- \[ = \left(x - 3\right) \ln{\left(x - 3 \right)} + \left(\frac{x^{2}}{2} - 3 x + \frac{9}{2}\right) \frac{d}{d x} \ln{\left(x - 3 \right)} + \frac{d}{d x} \frac{3 x}{2} + \frac{d}{d x} \left(- \frac{x^{2}}{4}\right) \]derivative algebraDifferentiate the polynomial part of the product. Simplify the polynomial term.✓ Proved
- \[ = \left(x - 3\right) \ln{\left(x - 3 \right)} + \frac{d}{d x} \frac{3 x}{2} + \frac{d}{d x} \left(- \frac{x^{2}}{4}\right) + \frac{\frac{x^{2}}{2} - 3 x + \frac{9}{2}}{x - 3} \]derivativeDifferentiate the logarithm.✓ Proved
- \[ = - \frac{x}{2} + \left(x - 3\right) \ln{\left(x - 3 \right)} + \frac{3}{2} + \frac{\frac{x^{2}}{2} - 3 x + \frac{9}{2}}{x - 3} \]derivative algebraEvaluate the derivatives of the power and linear terms. Simplify the first term.✓ Proved
- \[ = - \frac{x}{2} + \left(x - 3\right) \ln{\left(x - 3 \right)} + \frac{3}{2} + \frac{0.5 x^{2} - 3 x + 4.5}{x - 3} \]algebraRewrite coefficients for clarity.✓ Proved
- \[ = - \frac{x}{2} + \left(x - 3\right) \ln{\left(x - 3 \right)} + \frac{3}{2} + \frac{0.5 x^{2} - 3.0 x + 4.5}{x - 3} \]algebraFactor out 0.5 from the numerator.✓ Proved
- \[ = \left(x - 3\right) \ln{\left(x - 3 \right)} \]algebra algebra algebra algebra algebra simplifyFactor the quadratic expression. Cancel the common factor (x - 3). Distribute the 0.5. Convert 1.5 to a fraction. Group like terms. Combine all terms to get the final result.✓ Proved
Answer \( \left(x - 3\right) \ln{\left(x - 3 \right)} \)
✓ 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 |
| 6 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 log is undefined for non-positive arguments undefined where x - 3 = 0 |
| 7 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 log is undefined for non-positive arguments undefined where x - 3 = 0 |
| 8 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 log is undefined for non-positive arguments undefined where x - 3 = 0 |
| 9 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 log is undefined for non-positive arguments undefined where x - 3 = 0 |
| 10 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 log is undefined for non-positive arguments undefined where x - 3 = 0 |
| 11 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 log is undefined for non-positive arguments undefined where x - 3 = 0 |
| 12 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 log is undefined for non-positive arguments |
| 13 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 log is undefined for non-positive arguments |
| 14 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 log is undefined for non-positive arguments |
| 15 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 log is undefined for non-positive arguments |
| 16 | ✓ 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 provided vocabulary.
Every verdict on record (4)
qwen3.6:27b-mlx: pass 2026-10-05 — The solution correctly applies differentiation rules and algebraic simplifications. Each step adheres to the single-change constraint and uses valid labels from the provided vocabulary.gpt-oss:20b: pass 2026-10-05qwen3.6:27b-mlx: pass 2026-10-05 — 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: fail (style) 2026-10-05 — Step 7 applies the derivative to two separate terms in one step but labels it only as "derivative". According to the contract, each step must change only one thing; this step changes two terms simultaneously and should be split into separate derivative steps or labeled with the sum rule.
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 2026-10-05 with SymPy 1.14.0.