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Derivative of \( \displaystyle 80 x^{3} + 120 x^{2} + 60 x \)

Problem 2.1757 · medium

Differentiate \( \displaystyle f(x) = 80 x^{3} + 120 x^{2} + 60 x \).
  1. \[ \frac{d}{d x} \left(80 x^{3} + 120 x^{2} + 60 x\right) \]
    sumStart with the derivative of the entire function.✓ Proved
  2. \[ = \frac{d}{d x} 60 x + \frac{d}{d x} 120 x^{2} + \frac{d}{d x} 80 x^{3} \]
    sumApply the sum rule to differentiate each term separately.✓ Proved
  3. \[ = 60 \frac{d}{d x} x + 120 \frac{d}{d x} x^{2} + 80 \frac{d}{d x} x^{3} \]
    constant-multiplePull out the constant coefficients.✓ Proved
  4. \[ = 240 x^{2} + 240 x + 60 \]
    power algebraApply the power rule to each term. Multiply the constants.✓ Proved
Answer \( 60 \left(2 x + 1\right)^{2} \)

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
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)
  • gpt-oss:20b: pass 2026-10-07
  • qwen3.6:27b-mlx: pass 2026-10-07
  • gpt-oss:20b: fail (error) 2026-10-07 — Step 1 incorrectly labels the application of the sum rule. Taking the derivative of the entire expression is not a sum rule step; it should be a plain derivative. This mislabeling misleads the reader about the rule being applied.
  • qwen3.6:27b-mlx: pass 2026-10-07

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 2026-10-07 with SymPy 1.14.0.