Derivative of \( \displaystyle 2 x \left(- 2 x - 1\right) \)
Problem 2.693 · medium
Differentiate \( \displaystyle f(x) = 2 x \left(- 2 x - 1\right) \).
- \[ \frac{d}{d x} 2 x \left(- 2 x - 1\right) \]derivativeStart with the derivative of the function.✓ Proved
- \[ = 2 \frac{d}{d x} x \left(- 2 x - 1\right) \]constant-multiplePull out the constant factor 2.✓ Proved
- \[ = 2 x \frac{d}{d x} \left(- 2 x - 1\right) + 2 \left(- 2 x - 1\right) \frac{d}{d x} x \]productApply the product rule.✓ Proved
- \[ = 2 x \frac{d}{d x} \left(- 2 x - 1\right) - 4 x - 2 \]derivativeDifferentiate the first part of the product.✓ Proved
- \[ = - 8 x - 2 \]derivative algebra simplify algebraDifferentiate the second part of the product. Distribute the x into the derivative term. Combine like terms inside the parentheses. Distribute the 2 to get the final simplified form.✓ Proved
Answer \( - 8 x - 2 \)
✓ 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: pass — The solution correctly applies differentiation rules one at a time and uses valid labels from the fixed vocabulary. Each step is logically sound and algebraically correct.
Every verdict on record (4)
qwen3.6:27b-mlx: pass 2026-09-21 — The solution correctly applies differentiation rules one at a time and uses valid labels from the fixed vocabulary. Each step is logically sound and algebraically correct.gpt-oss:20b: pass 2026-09-21qwen3.6:27b-mlx: pass 2026-09-21 — The solution correctly applies the constant multiple, product, and derivative rules in a step-by-step manner. Each step changes only one aspect of the expression and uses valid labels from the provided vocabulary.gpt-oss:20b: pass 2026-09-21
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.