Derivative of \( \displaystyle 2 x \left(3 - x\right) \)
Problem 2.1103 · medium
Differentiate \( \displaystyle f(x) = 2 x \left(3 - x\right) \).
- \[ \frac{d}{d x} 2 x \left(3 - x\right) \]derivativeStart with the derivative of the function.✓ Proved
- \[ = \frac{d}{d x} \left(- 2 x^{2} + 6 x\right) \]algebraExpand the expression.✓ Proved
- \[ = \frac{d}{d x} 6 x - \frac{d}{d x} 2 x^{2} \]sumApply the difference rule.✓ Proved
- \[ = 6 \frac{d}{d x} x - 2 \frac{d}{d x} x^{2} \]constantApply the constant multiple rule.✓ Proved
- \[ = 6 - 2 \frac{d}{d x} x^{2} \]derivative algebraDifferentiate the first term. Simplify the first term.✓ Proved
- \[ = 6 - 4 x \]power algebraApply the power rule to the second term. Multiply the constants.✓ Proved
Answer \( 6 - 4 x \)
✓ 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 |
| 3 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 |
| 4 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 |
| 5 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 |
| 6 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 |
| 7 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 |
| 8 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 |
| answer | ✓ Proved | sympy 1.14.0 | final line against the stated answer: simplify(a - b) reduced to 0 |
| 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: fail (style) — Step 4 is labeled 'constant' but applies the constant multiple rule; the correct label from the vocabulary is 'constant-multiple'.
Every verdict on record (4)
qwen3.6:27b-mlx: fail (style) 2026-09-28 — Step 4 is labeled 'constant' but applies the constant multiple rule; the correct label from the vocabulary is 'constant-multiple'.gpt-oss:20b: pass 2026-09-28qwen3.6:27b-mlx: fail (style) 2026-09-28 — Step 4 applies the constant multiple rule to both terms simultaneously, violating the one-change-per-step constraint. Step 3 labels the difference rule as 'sum', which is acceptable per the contract, but Step 4's granularity is the primary defect.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.