Derivative of \( \displaystyle - x^{3} - 3 x^{2} - 3 x \)
Problem 2.2076 · medium
Differentiate \( \displaystyle f(x) = - x^{3} - 3 x^{2} - 3 x \).
- \[ \frac{d}{d x} \left(- x^{3} - 3 x^{2} - 3 x\right) \]derivativeStart with the derivative of the function.✓ Proved
- \[ = \frac{d}{d x} \left(- 3 x\right) + \frac{d}{d x} \left(- 3 x^{2}\right) + \frac{d}{d x} \left(- x^{3}\right) \]sumApply the sum rule to differentiate each term separately.✓ Proved
- \[ = - 3 \frac{d}{d x} x - 3 \frac{d}{d x} x^{2} - \frac{d}{d x} x^{3} \]constantFactor out the negative signs.✓ Proved
- \[ = - 3 x^{2} - 6 x - 3 \]power algebraApply the power rule to each term. Simplify the coefficients.✓ Proved
Answer \( - 3 \left(x + 1\right)^{2} \)
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
| 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 |
| 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)
gpt-oss:20b: pass 2026-10-11qwen3.6:27b-mlx: pass 2026-10-11gpt-oss:20b: pass 2026-10-11qwen3.6:27b-mlx: fail (error) 2026-10-11 — Step 3 applies both the constant multiple rule (to factor out -3) and the constant rule (to factor out -1) simultaneously, violating the one-rule-per-step constraint. Additionally, the label 'constant' is incorrect for factoring out negative signs; this should be labeled 'constant-multiple'.
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 2026-10-11 with SymPy 1.14.0.