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Derivative of \( \displaystyle 3 x \left(- 3 x^{2} - 6 x - 4\right) \)

Problem 2.1407 · hard

Differentiate \( \displaystyle f(x) = 3 x \left(- 3 x^{2} - 6 x - 4\right) \).
  1. \[ \frac{d}{d x} 3 x \left(- 3 x^{2} - 6 x - 4\right) \]
    Start with the derivative of the function.✓ Proved
  2. \[ = 3 x \frac{d}{d x} \left(- 3 x^{2} - 6 x - 4\right) + \left(- 3 x^{2} - 6 x - 4\right) \frac{d}{d x} 3 x \]
    productApply the product rule.✓ Proved
  3. \[ = - 9 x^{2} + 3 x \frac{d}{d x} \left(- 3 x^{2} - 6 x - 4\right) - 18 x - 12 \]
    derivativeDifferentiate the first part of the product.✓ Proved
  4. \[ = - 9 x^{2} - 3 x \frac{d}{d x} 4 - 3 x \frac{d}{d x} 6 x + 3 x \frac{d}{d x} \left(- 3 x^{2}\right) - 18 x - 12 \]
    sumDistribute the derivative over the sum.✓ Proved
  5. \[ = - 27 x^{2} - 36 x - 12 \]
    derivative algebra constant-multiple simplifyDifferentiate each term in the sum. Simplify the terms. Distribute the 3. Combine like terms.✓ Proved
Answer \( - 3 \left(3 x + 2\right)^{2} \)

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
3✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
4✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
5✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
6✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
7✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
8✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
answer✓ Provedsympy 1.14.0final line against the stated answer: simplify(a - b) reduced to 0
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
Every verdict on record (4)
  • qwen3.6:27b-mlx: pass 2026-10-03
  • gpt-oss:20b: pass 2026-10-03
  • qwen3.6:27b-mlx: pass 2026-10-03 — The solution correctly applies the product rule, linearity of the derivative, and basic differentiation rules. Each step changes only one aspect of the expression, and the labels accurately reflect the operations performed.
  • gpt-oss:20b: fail (error) 2026-10-03 — Step 4 incorrectly distributes the derivative over the sum: the term –6*x is treated as +6*x, leading to a sign error in subsequent steps. The derivative of –6*x should be –6, not +6.

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 2026-10-03 with SymPy 1.14.0.