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Derivative of \( \displaystyle \left(x - \frac{1}{2}\right) e^{4 x - 1} \)

Problem 2.1380 · medium

Differentiate \( \displaystyle f(x) = \left(x - \frac{1}{2}\right) e^{4 x - 1} \).
  1. \[ \frac{d}{d x} \left(x - \frac{1}{2}\right) e^{4 x - 1} \]
    Start with the derivative of the function.✓ Proved
  2. \[ = \frac{d}{d x} \left(x e^{4 x - 1} - \frac{e^{4 x - 1}}{2}\right) \]
    algebraDistribute the term (x - 1/2).✓ Proved
  3. \[ = \frac{d}{d x} x e^{4 x - 1} - \frac{d}{d x} \frac{e^{4 x - 1}}{2} \]
    sumApply the sum rule for differentiation.✓ Proved
  4. \[ = \frac{d}{d x} x e^{4 x - 1} - \frac{\frac{d}{d x} e^{4 x - 1}}{2} \]
    constantPull out the constant factor 1/2.✓ Proved
  5. \[ = x \frac{d}{d x} e^{4 x - 1} + e^{4 x - 1} \frac{d}{d x} x - \frac{\frac{d}{d x} e^{4 x - 1}}{2} \]
    productApply the product rule to the first term.✓ Proved
  6. \[ = x \frac{d}{d x} e^{4 x - 1} + e^{4 x - 1} - \frac{\frac{d}{d x} e^{4 x - 1}}{2} \]
    derivative constantDifferentiate x. Simplify 1*exp(4*x - 1).✓ Proved
  7. \[ = \left(x - \frac{1}{2}\right) \frac{d}{d x} e^{4 x - 1} + e^{4 x - 1} \]
    algebraFactor out the common derivative term.✓ Proved
  8. \[ = \left(x - \frac{1}{2}\right) e^{4 x - 1} \frac{d}{d x} \left(4 x - 1\right) + e^{4 x - 1} \]
    chainApply the chain rule to the exponential term.✓ Proved
  9. \[ = 4 \left(x - \frac{1}{2}\right) e^{4 x - 1} + e^{4 x - 1} \]
    derivativeDifferentiate the inner function 4*x - 1.✓ Proved
  10. \[ = \left(4 x - 2\right) e^{4 x - 1} + e^{4 x - 1} \]
    algebraDistribute the 4 into the parentheses.✓ Proved
  11. \[ = \left(4 x - 1\right) e^{4 x - 1} \]
    algebra simplifyFactor out the common exp(4*x - 1) term. Combine the terms inside the parentheses.✓ Proved
Answer \( \left(4 x - 1\right) e^{4 x - 1} \)

✓ 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
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
10✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
11✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
12✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
13✓ 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
  • qwen3.6:27b-mlx: pass
Every verdict on record (4)
  • qwen3.6:27b-mlx: pass 2026-10-03
  • gpt-oss:20b: pass 2026-10-03
  • qwen3.6:27b-mlx: fail (style) 2026-10-03 — Step 4 is labeled 'constant' but applies the constant-multiple rule (pulling out a factor); the vocabulary requires 'constant-multiple' for this operation. Step 7 is labeled 'constant' but performs algebraic simplification (1*exp -> exp), which should be labeled 'algebra' or 'simplify'.
  • gpt-oss:20b: pass 2026-10-03

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 2026-10-03 with SymPy 1.14.0.