Derivative of \( \displaystyle 20 x^{3} - 90 x^{2} + 135 x \)
Problem 2.1766 · medium
Differentiate \( \displaystyle f(x) = 20 x^{3} - 90 x^{2} + 135 x \).
- \[ \frac{d}{d x} \left(20 x^{3} - 90 x^{2} + 135 x\right) \]derivativeStart with the derivative of the function.✓ Proved
- \[ = \frac{d}{d x} 135 x - \frac{d}{d x} 90 x^{2} + \frac{d}{d x} 20 x^{3} \]sumApply the sum rule.✓ Proved
- \[ = 135 \frac{d}{d x} x - 90 \frac{d}{d x} x^{2} + 20 \frac{d}{d x} x^{3} \]constant-multipleFactor out the constants.✓ Proved
- \[ = 60 x^{2} - 180 x + 135 \]power algebraApply the power rule to each term. Multiply the coefficients.✓ Proved
Answer \( 15 \left(2 x - 3\right)^{2} \)
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 2026-10-07qwen3.6:27b-mlx: pass 2026-10-07gpt-oss:20b: fail (error) 2026-10-07 — The solution stops at 60*x**2 - 180*x + 135 but the stated answer is 15*(2*x - 3)**2. A missing step that factors or rewrites the polynomial into the given form is required; without it the solution is incomplete.qwen3.6:27b-mlx: pass 2026-10-07
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 2026-10-07 with SymPy 1.14.0.