Derivative of \( \displaystyle 15 x \left(3 x^{2} - 3 x + 1\right) \)
Problem 2.989 · hard
Differentiate \( \displaystyle f(x) = 15 x \left(3 x^{2} - 3 x + 1\right) \).
- \[ \frac{d}{d x} 15 x \left(3 x^{2} - 3 x + 1\right) \]Start with the derivative of the function.✓ Proved
- \[ = \frac{d}{d x} \left(45 x^{3} - 45 x^{2} + 15 x\right) \]algebraDistribute the 15*x into the parentheses.✓ Proved
- \[ = \frac{d}{d x} 15 x - \frac{d}{d x} 45 x^{2} + \frac{d}{d x} 45 x^{3} \]sumApply the sum rule for differentiation.✓ Proved
- \[ = 15 \frac{d}{d x} x - 45 \frac{d}{d x} x^{2} + 45 \frac{d}{d x} x^{3} \]constant-multipleFactor out the constants from each term.✓ Proved
- \[ = 135 x^{2} - 90 x + 15 \]power simplifyApply the power rule to each term. Multiply the coefficients to get the final result.✓ Proved
Answer \( 15 \left(3 x - 1\right)^{2} \)
✓ 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 |
| 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 the rules in sequence: algebraic expansion, linearity of the derivative (sum and constant-multiple), power rule, and simplification. Each step changes only one aspect of the expression and uses valid labels from the fixed vocabulary.
Every verdict on record (4)
qwen3.6:27b-mlx: pass 2026-09-27 — The solution correctly applies the rules in sequence: algebraic expansion, linearity of the derivative (sum and constant-multiple), power rule, and simplification. Each step changes only one aspect of the expression and uses valid labels from the fixed vocabulary.gpt-oss:20b: pass 2026-09-27qwen3.6:27b-mlx: pass 2026-09-27 — The solution correctly applies the one-change-per-step constraint. Step 2 performs algebraic expansion inside the derivative operator, which is a valid 'algebra' step. Subsequent steps correctly apply sum, constant-multiple, and power rules. The final result matches the stated answer.gpt-oss:20b: pass 2026-09-27
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 2026-09-27 with SymPy 1.14.0.