Derivative of \( \displaystyle - \frac{x^{2}}{2} + x \left(x - 6\right) \ln{\left(x - 3 \right)} + 3 x + 9 \ln{\left(x - 3 \right)} \)
Problem 2.1064 · hard
Differentiate \( \displaystyle f(x) = - \frac{x^{2}}{2} + x \left(x - 6\right) \ln{\left(x - 3 \right)} + 3 x + 9 \ln{\left(x - 3 \right)} \).
- \[ \frac{d}{d x} \left(- \frac{x^{2}}{2} + x \left(x - 6\right) \ln{\left(x - 3 \right)} + 3 x + 9 \ln{\left(x - 3 \right)}\right) \]derivativeStart with the derivative of the function.✓ Proved
- \[ = \frac{d}{d x} 3 x + \frac{d}{d x} \left(- \frac{x^{2}}{2}\right) + \frac{d}{d x} x \left(x - 6\right) \ln{\left(x - 3 \right)} + \frac{d}{d x} 9 \ln{\left(x - 3 \right)} \]sumApply the sum rule.✓ Proved
- \[ = \frac{d}{d x} \left(- \frac{x^{2}}{2}\right) + \frac{d}{d x} x \left(x - 6\right) \ln{\left(x - 3 \right)} + \frac{d}{d x} 9 \ln{\left(x - 3 \right)} + 3 \]constantDifferentiate the linear term 3*x.✓ Proved
- \[ = \frac{d}{d x} \left(- \frac{x^{2}}{2}\right) + \frac{d}{d x} x \left(x - 6\right) \ln{\left(x - 3 \right)} + 9 \frac{d}{d x} \ln{\left(x - 3 \right)} + 3 \]constant-multiplePull out the constant 9.✓ Proved
- \[ = \frac{d}{d x} \left(- \frac{x^{2}}{2}\right) + \frac{d}{d x} x \left(x - 6\right) \ln{\left(x - 3 \right)} + 3 + \frac{9 \frac{d}{d x} \left(x - 3\right)}{x - 3} \]chainApply the chain rule to log(x - 3).✓ Proved
- \[ = \frac{d}{d x} \left(- \frac{x^{2}}{2}\right) + \frac{d}{d x} x \left(x - 6\right) \ln{\left(x - 3 \right)} + 3 + \frac{9}{x - 3} \]derivative algebraDifferentiate x - 3. Simplify the expression.✓ Proved
- \[ = - x + \frac{d}{d x} x \left(x - 6\right) \ln{\left(x - 3 \right)} + 3 + \frac{9}{x - 3} \]derivativeDifferentiate -x**2/2.✓ Proved
- \[ = x \left(x - 6\right) \frac{d}{d x} \ln{\left(x - 3 \right)} - x + \ln{\left(x - 3 \right)} \frac{d}{d x} x \left(x - 6\right) + 3 + \frac{9}{x - 3} \]productApply the product rule to x*(x - 6)*log(x - 3).✓ Proved
- \[ = x \left(x - 6\right) \frac{d}{d x} \ln{\left(x - 3 \right)} - x + \left(x \frac{d}{d x} \left(x - 6\right) + \left(x - 6\right) \frac{d}{d x} x\right) \ln{\left(x - 3 \right)} + 3 + \frac{9}{x - 3} \]productApply the product rule to (x*(x - 6))*log(x - 3).✓ Proved
- \[ = x \left(x - 6\right) \frac{d}{d x} \ln{\left(x - 3 \right)} - x + \left(2 x - 6\right) \ln{\left(x - 3 \right)} + 3 + \frac{9}{x - 3} \]derivative algebra algebraDifferentiate the components of the product rule. Simplify the expression inside the parentheses. Combine like terms.✓ Proved
- \[ = \frac{x \left(x - 6\right)}{x - 3} - x + \left(2 x - 6\right) \ln{\left(x - 3 \right)} + 3 + \frac{9}{x - 3} \]derivativeDifferentiate log(x - 3).✓ Proved
- \[ = - x + \left(2 x - 6\right) \ln{\left(x - 3 \right)} + 3 + \frac{x^{2} - 6 x}{x - 3} + \frac{9}{x - 3} \]algebraMultiply the terms.✓ Proved
- \[ = - x + \left(2 x - 6\right) \ln{\left(x - 3 \right)} + \frac{x^{2} - 3 x}{x - 3} \]algebra algebra algebraFind a common denominator for the rational terms. Expand the numerator. Simplify the numerator.✓ Proved
- \[ = \left(2 x - 6\right) \ln{\left(x - 3 \right)} \]algebra algebra algebraFactor the numerator. Cancel the common factor (x - 3). Final simplification.✓ Proved
Answer \( 2 \left(x - 3\right) \ln{\left(x - 3 \right)} \)
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
| 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 - 3 = 0 |
| 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 undefined where x - 3 = 0 |
| 13 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 log is undefined for non-positive arguments undefined where x - 3 = 0 |
| 14 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 log is undefined for non-positive arguments undefined where x - 3 = 0 |
| 15 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 log is undefined for non-positive arguments undefined where x - 3 = 0 |
| 16 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 log is undefined for non-positive arguments undefined where x - 3 = 0 |
| 17 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 log is undefined for non-positive arguments undefined where x - 3 = 0 |
| 18 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 log is undefined for non-positive arguments undefined where x - 3 = 0 |
| 19 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 log is undefined for non-positive arguments undefined where x - 3 = 0 |
| 20 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 log is undefined for non-positive arguments |
| 21 | ✓ 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 in single-step increments. The labels used are appropriate for the operations performed.
Every verdict on record (4)
qwen3.6:27b-mlx: pass 2026-09-28 — The solution correctly applies differentiation rules and algebraic simplifications in single-step increments. The labels used are appropriate for the operations performed.gpt-oss:20b: pass 2026-09-28qwen3.6:27b-mlx: inconclusive 2026-09-28 — reviewer response could not be parsed: { "verdict": "fail", "severity": "error", "notes": "Step 9 applies the product rule to a three-factor term x*(x-6)*log(x-3) by splitting it into two parts, but Step 10 immediately re-applies thegpt-oss:20b: pass 2026-09-28
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 2026-09-28 with SymPy 1.14.0.