Derivative of \( \displaystyle \left(x - \frac{1}{2}\right) e^{4 x - 1} \)
Problem 2.1380 · medium
Differentiate \( \displaystyle f(x) = \left(x - \frac{1}{2}\right) e^{4 x - 1} \).
- \[ \frac{d}{d x} \left(x - \frac{1}{2}\right) e^{4 x - 1} \]Start with the derivative of the function.✓ Proved
- \[ = \frac{d}{d x} \left(x e^{4 x - 1} - \frac{e^{4 x - 1}}{2}\right) \]algebraDistribute the term (x - 1/2).✓ Proved
- \[ = \frac{d}{d x} x e^{4 x - 1} - \frac{d}{d x} \frac{e^{4 x - 1}}{2} \]sumApply the sum rule for differentiation.✓ Proved
- \[ = \frac{d}{d x} x e^{4 x - 1} - \frac{\frac{d}{d x} e^{4 x - 1}}{2} \]constantPull out the constant factor 1/2.✓ Proved
- \[ = x \frac{d}{d x} e^{4 x - 1} + e^{4 x - 1} \frac{d}{d x} x - \frac{\frac{d}{d x} e^{4 x - 1}}{2} \]productApply the product rule to the first term.✓ Proved
- \[ = x \frac{d}{d x} e^{4 x - 1} + e^{4 x - 1} - \frac{\frac{d}{d x} e^{4 x - 1}}{2} \]derivative constantDifferentiate x. Simplify 1*exp(4*x - 1).✓ Proved
- \[ = \left(x - \frac{1}{2}\right) \frac{d}{d x} e^{4 x - 1} + e^{4 x - 1} \]algebraFactor out the common derivative term.✓ Proved
- \[ = \left(x - \frac{1}{2}\right) e^{4 x - 1} \frac{d}{d x} \left(4 x - 1\right) + e^{4 x - 1} \]chainApply the chain rule to the exponential term.✓ Proved
- \[ = 4 \left(x - \frac{1}{2}\right) e^{4 x - 1} + e^{4 x - 1} \]derivativeDifferentiate the inner function 4*x - 1.✓ Proved
- \[ = \left(4 x - 2\right) e^{4 x - 1} + e^{4 x - 1} \]algebraDistribute the 4 into the parentheses.✓ Proved
- \[ = \left(4 x - 1\right) e^{4 x - 1} \]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
| 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 |
| 10 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 |
| 11 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 |
| 12 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 |
| 13 | ✓ 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)
qwen3.6:27b-mlx: pass 2026-10-03gpt-oss:20b: pass 2026-10-03qwen3.6:27b-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.