Derivative of \( \displaystyle 2 x \left(x^{2} + 6 x + 12\right) \)
Problem 2.829 · hard Beautiful
Differentiate \( \displaystyle f(x) = 2 x \left(x^{2} + 6 x + 12\right) \).
- \[ \frac{d}{d x} 2 x \left(x^{2} + 6 x + 12\right) \]derivativeStart with the derivative of the function.✓ Proved
- \[ = \frac{d}{d x} \left(2 x^{3} + 12 x^{2} + 24 x\right) \]algebraExpand the expression using distributive property.✓ Proved
- \[ = \frac{d}{d x} 24 x + \frac{d}{d x} 12 x^{2} + \frac{d}{d x} 2 x^{3} \]sumApply the sum rule for derivatives.✓ Proved
- \[ = 6 x^{2} + \frac{d}{d x} 24 x + \frac{d}{d x} 12 x^{2} \]powerDifferentiate the first term using the power rule.✓ Proved
- \[ = 6 x^{2} + 24 x + \frac{d}{d x} 24 x \]powerDifferentiate the second term using the power rule.✓ Proved
- \[ = 6 x^{2} + 24 x + 24 \]power simplifyDifferentiate the third term using the power rule. Factor the expression to show the simplified form.✓ Proved
Answer \( 6 \left(x + 2\right)^{2} \)
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
| 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 |
| 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: pass
Every verdict on record (4)
qwen3.6:27b-mlx: pass 2026-09-26gpt-oss:20b: pass 2026-09-26qwen3.6:27b-mlx: pass 2026-09-26gpt-oss:20b: fail (error) 2026-09-26 — Step 1 applies the derivative rule directly to the product 2*x*(x**2+6*x+12) without using the product rule, which is a multi‑rule application and incorrect. The correct first step would be to apply the product rule, not a single derivative rule.
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 2026-09-26 with SymPy 1.14.0.