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Derivative of \( \displaystyle \left(\frac{1}{2} - x\right) e^{2 x} \)

Problem 2.166 · hard

Differentiate \( \displaystyle f(x) = \left(\frac{1}{2} - x\right) e^{2 x} \).
  1. \[ \frac{d}{d x} \left(\frac{1}{2} - x\right) e^{2 x} \]
    derivativeStart with the derivative of the function.✓ Proved
  2. \[ = \frac{d}{d x} \left(- x e^{2 x} + \frac{e^{2 x}}{2}\right) \]
    algebraDistribute the term.✓ Proved
  3. \[ = - \frac{d}{d x} x e^{2 x} + \frac{d}{d x} \frac{e^{2 x}}{2} \]
    sumApply the difference rule.✓ Proved
  4. \[ = - \frac{d}{d x} x e^{2 x} + \frac{\frac{d}{d x} e^{2 x}}{2} \]
    constant-multipleFactor out the constant.✓ Proved
  5. \[ = - x \frac{d}{d x} e^{2 x} - e^{2 x} \frac{d}{d x} x + \frac{\frac{d}{d x} e^{2 x}}{2} \]
    productApply the product rule to the second term.✓ Proved
  6. \[ = - 2 x e^{2 x} \]
    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
LineStatusChecked byDetail
1✓ Provedsympy 1.14.0line 1 is the problem as stated
2✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
3✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
4✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
5✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
6✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
7✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
8✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
9✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
answer✓ Provedsympy 1.14.0final line against the stated answer: simplify(a - b) reduced to 0
answer, a second way✓ Provedsympy 1.14.0SymPy differentiated f directly and got the stated answer

Reviewers

  • gpt-oss:20b: pass
  • deepseek-r1:70b: pass
  • qwen3.6:27b-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 2026-09-20
  • qwen3.6:27b-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 2026-09-20
  • qwen3.6:27b-mlx: pass 2026-09-19
  • deepseek-r1:70b: pass 2026-09-19
  • gpt-oss:20b: pass 2026-09-19
  • qwen3.6:27b-mlx: pass 2026-09-19
  • deepseek-r1:70b: pass 2026-09-19
  • gpt-oss:20b: pass 2026-09-19
  • qwen3.6:27b-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 2026-09-18
  • gpt-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.