Derivative of \( \displaystyle \left(\frac{1}{2} - x\right) e^{2 x} \)
Problem 2.166 · hard
Differentiate \( \displaystyle f(x) = \left(\frac{1}{2} - x\right) e^{2 x} \).
- \[ \frac{d}{d x} \left(\frac{1}{2} - x\right) e^{2 x} \]derivativeStart with the derivative of the function.✓ Proved
- \[ = \frac{d}{d x} \left(- x e^{2 x} + \frac{e^{2 x}}{2}\right) \]algebraDistribute the term.✓ Proved
- \[ = - \frac{d}{d x} x e^{2 x} + \frac{d}{d x} \frac{e^{2 x}}{2} \]sumApply the difference rule.✓ Proved
- \[ = - \frac{d}{d x} x e^{2 x} + \frac{\frac{d}{d x} e^{2 x}}{2} \]constant-multipleFactor out the constant.✓ Proved
- \[ = - x \frac{d}{d x} e^{2 x} - e^{2 x} \frac{d}{d x} x + \frac{\frac{d}{d x} e^{2 x}}{2} \]productApply the product rule to the second term.✓ Proved
- \[ = - 2 x e^{2 x} \]chain simplify algebra simplifyApply the chain rule to the exponential terms. Simplify the coefficients. Distribute the negative sign. Combine like terms.✓ Proved
Answer \( - 2 x e^{2 x} \)
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 |
| 8 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 |
| 9 | ✓ 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: passdeepseek-r1:70b: passqwen3.6:27b-mlx: fail (error) — Step 6 applies the chain rule to both exponential terms simultaneously, violating the single-rule-per-step constraint. Additionally, the label 'chain' is incorrect for the differentiation of x (Derivative(x, x) -> 1), which is a basic derivative, not a chain rule application.
Every verdict on record (15)
qwen3.6:27b-mlx: fail (error) 2026-09-20 — Step 6 applies the chain rule to both exponential terms simultaneously, violating the single-rule-per-step constraint. Additionally, the label 'chain' is incorrect for the differentiation of x (Derivative(x, x) -> 1), which is a basic derivative, not a chain rule application.gpt-oss:20b: pass 2026-09-20qwen3.6:27b-mlx: fail (style) 2026-09-20 — Step 6 applies the chain rule to both exponential terms simultaneously, violating the one-change-per-step constraint. It should be split into two steps.gpt-oss:20b: pass 2026-09-20qwen3.6:27b-mlx: pass 2026-09-19deepseek-r1:70b: pass 2026-09-19gpt-oss:20b: pass 2026-09-19qwen3.6:27b-mlx: pass 2026-09-19deepseek-r1:70b: pass 2026-09-19gpt-oss:20b: pass 2026-09-19qwen3.6:27b-mlx: fail (error) 2026-09-18 — Step 6 applies the chain rule to both exponential terms simultaneously, violating the one-rule-per-step constraint. Additionally, the label 'chain' is insufficient because the step also evaluates the derivatives of the inner functions (e.g., d/dx(2x) = 2) and the outer exponential, which are distinct differentiation rules.deepseek-r1:70b: pass 2026-09-18gpt-oss:20b: fail (error) 2026-09-18 — Step 6 applies the chain rule twice in a single line, changing two terms at once. Each step should modify only one part of the expression.gpt-oss:20b: fail 2026-09-17 — Step 3 incorrectly labels the rule as "sum" while actually applying the difference rule, which misleads the student about the rule being used.deepseek-r1:70b: pass 2026-09-17
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.