∫Calc Practice
Home›Calculus 1›Product rule›Problem 2.1064

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 \( \displaystyle f(x) = - \frac{x^{2}}{2} + x \left(x - 6\right) \ln{\left(x - 3 \right)} + 3 x + 9 \ln{\left(x - 3 \right)} \).
  1. \[ \frac{d}{d x} \left(- \frac{x^{2}}{2} + x \left(x - 6\right) \ln{\left(x - 3 \right)} + 3 x + 9 \ln{\left(x - 3 \right)}\right) \]
    derivativeStart with the derivative of the function.✓ Proved
  2. \[ = \frac{d}{d x} 3 x + \frac{d}{d x} \left(- \frac{x^{2}}{2}\right) + \frac{d}{d x} x \left(x - 6\right) \ln{\left(x - 3 \right)} + \frac{d}{d x} 9 \ln{\left(x - 3 \right)} \]
    sumApply the sum rule.✓ Proved
  3. \[ = \frac{d}{d x} \left(- \frac{x^{2}}{2}\right) + \frac{d}{d x} x \left(x - 6\right) \ln{\left(x - 3 \right)} + \frac{d}{d x} 9 \ln{\left(x - 3 \right)} + 3 \]
    constantDifferentiate the linear term 3*x.✓ Proved
  4. \[ = \frac{d}{d x} \left(- \frac{x^{2}}{2}\right) + \frac{d}{d x} x \left(x - 6\right) \ln{\left(x - 3 \right)} + 9 \frac{d}{d x} \ln{\left(x - 3 \right)} + 3 \]
    constant-multiplePull out the constant 9.✓ Proved
  5. \[ = \frac{d}{d x} \left(- \frac{x^{2}}{2}\right) + \frac{d}{d x} x \left(x - 6\right) \ln{\left(x - 3 \right)} + 3 + \frac{9 \frac{d}{d x} \left(x - 3\right)}{x - 3} \]
    chainApply the chain rule to log(x - 3).✓ Proved
  6. \[ = \frac{d}{d x} \left(- \frac{x^{2}}{2}\right) + \frac{d}{d x} x \left(x - 6\right) \ln{\left(x - 3 \right)} + 3 + \frac{9}{x - 3} \]
    derivative algebraDifferentiate x - 3. Simplify the expression.✓ Proved
  7. \[ = - x + \frac{d}{d x} x \left(x - 6\right) \ln{\left(x - 3 \right)} + 3 + \frac{9}{x - 3} \]
    derivativeDifferentiate -x**2/2.✓ Proved
  8. \[ = x \left(x - 6\right) \frac{d}{d x} \ln{\left(x - 3 \right)} - x + \ln{\left(x - 3 \right)} \frac{d}{d x} x \left(x - 6\right) + 3 + \frac{9}{x - 3} \]
    productApply the product rule to x*(x - 6)*log(x - 3).✓ Proved
  9. \[ = x \left(x - 6\right) \frac{d}{d x} \ln{\left(x - 3 \right)} - x + \left(x \frac{d}{d x} \left(x - 6\right) + \left(x - 6\right) \frac{d}{d x} x\right) \ln{\left(x - 3 \right)} + 3 + \frac{9}{x - 3} \]
    productApply the product rule to (x*(x - 6))*log(x - 3).✓ Proved
  10. \[ = x \left(x - 6\right) \frac{d}{d x} \ln{\left(x - 3 \right)} - x + \left(2 x - 6\right) \ln{\left(x - 3 \right)} + 3 + \frac{9}{x - 3} \]
    derivative algebra algebraDifferentiate the components of the product rule. Simplify the expression inside the parentheses. Combine like terms.✓ Proved
  11. \[ = \frac{x \left(x - 6\right)}{x - 3} - x + \left(2 x - 6\right) \ln{\left(x - 3 \right)} + 3 + \frac{9}{x - 3} \]
    derivativeDifferentiate log(x - 3).✓ Proved
  12. \[ = - x + \left(2 x - 6\right) \ln{\left(x - 3 \right)} + 3 + \frac{x^{2} - 6 x}{x - 3} + \frac{9}{x - 3} \]
    algebraMultiply the terms.✓ Proved
  13. \[ = - x + \left(2 x - 6\right) \ln{\left(x - 3 \right)} + \frac{x^{2} - 3 x}{x - 3} \]
    algebra algebra algebraFind a common denominator for the rational terms. Expand the numerator. Simplify the numerator.✓ Proved
  14. \[ = \left(2 x - 6\right) \ln{\left(x - 3 \right)} \]
    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
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 - 3 = 0
6✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
log is undefined for non-positive arguments
undefined where x - 3 = 0
7✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
log is undefined for non-positive arguments
undefined where x - 3 = 0
8✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
log is undefined for non-positive arguments
undefined where x - 3 = 0
9✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
log is undefined for non-positive arguments
undefined where x - 3 = 0
10✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
log is undefined for non-positive arguments
undefined where x - 3 = 0
11✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
log is undefined for non-positive arguments
undefined where x - 3 = 0
12✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
log is undefined for non-positive arguments
undefined where x - 3 = 0
13✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
log is undefined for non-positive arguments
undefined where x - 3 = 0
14✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
log is undefined for non-positive arguments
undefined where x - 3 = 0
15✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
log is undefined for non-positive arguments
undefined where x - 3 = 0
16✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
log is undefined for non-positive arguments
undefined where x - 3 = 0
17✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
log is undefined for non-positive arguments
undefined where x - 3 = 0
18✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
log is undefined for non-positive arguments
undefined where x - 3 = 0
19✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
log is undefined for non-positive arguments
undefined where x - 3 = 0
20✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
log is undefined for non-positive arguments
21✓ 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 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 2026-09-28
  • qwen3.6:27b-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 the
  • gpt-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.