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Derivative of \( \displaystyle \frac{\left(\sin{\left(4 x + 1 \right)} - \cos{\left(4 x + 1 \right)}\right) e^{4 x + 1}}{8} \)

Problem 2.1030 · hard

Differentiate \( \displaystyle f(x) = \frac{\left(\sin{\left(4 x + 1 \right)} - \cos{\left(4 x + 1 \right)}\right) e^{4 x + 1}}{8} \).
  1. \[ \frac{d}{d x} \frac{\left(\sin{\left(4 x + 1 \right)} - \cos{\left(4 x + 1 \right)}\right) e^{4 x + 1}}{8} \]
    derivativeStart with the derivative of the function.✓ Proved
  2. \[ = \left(\sin{\left(4 x + 1 \right)} - \cos{\left(4 x + 1 \right)}\right) \frac{d}{d x} \frac{e^{4 x + 1}}{8} + \frac{e^{4 x + 1} \frac{d}{d x} \left(\sin{\left(4 x + 1 \right)} - \cos{\left(4 x + 1 \right)}\right)}{8} \]
    productApply the product rule.✓ Proved
  3. \[ = \frac{\left(\sin{\left(4 x + 1 \right)} - \cos{\left(4 x + 1 \right)}\right) \frac{d}{d x} e^{4 x + 1}}{8} + \frac{e^{4 x + 1} \frac{d}{d x} \left(\sin{\left(4 x + 1 \right)} - \cos{\left(4 x + 1 \right)}\right)}{8} \]
    constantPull out the constant factor 1/8.✓ Proved
  4. \[ = \frac{\left(\sin{\left(4 x + 1 \right)} - \cos{\left(4 x + 1 \right)}\right) \frac{d}{d x} e^{4 x + 1}}{8} + \frac{\left(\frac{d}{d x} \sin{\left(4 x + 1 \right)} - \frac{d}{d x} \cos{\left(4 x + 1 \right)}\right) e^{4 x + 1}}{8} \]
    sumApply the sum rule to the first term.✓ Proved
  5. \[ = \frac{\left(\sin{\left(4 x + 1 \right)} - \cos{\left(4 x + 1 \right)}\right) e^{4 x + 1}}{2} + \frac{\left(4 \sin{\left(4 x + 1 \right)} + 4 \cos{\left(4 x + 1 \right)}\right) e^{4 x + 1}}{8} \]
    chain algebraApply the chain rule to the trigonometric and exponential terms. Simplify the signs.✓ Proved
  6. \[ = \frac{\left(\sin{\left(4 x + 1 \right)} - \cos{\left(4 x + 1 \right)}\right) e^{4 x + 1}}{2} + \frac{\left(\sin{\left(4 x + 1 \right)} + \cos{\left(4 x + 1 \right)}\right) e^{4 x + 1}}{2} \]
    simplifySimplify the coefficients.✓ Proved
  7. \[ = e^{4 x + 1} \sin{\left(4 x + 1 \right)} \]
    algebra simplify simplifyFactor out the common term exp(4*x + 1) / 2. Combine like terms inside the parentheses. Final simplification.✓ Proved
Answer \( e^{4 x + 1} \sin{\left(4 x + 1 \right)} \)

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
10✓ 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 2026-09-27
  • gpt-oss:20b: pass 2026-09-27
  • qwen3.6:27b-mlx: pass 2026-09-27
  • gpt-oss:20b: fail (error) 2026-09-27 — Step 5 applies the chain rule to both the sin and cos terms in a single line, effectively performing two derivative operations at once. This violates the rule that each step must change only one thing and apply only one named rule.

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 2026-09-27 with SymPy 1.14.0.