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Derivative of \( \displaystyle - \frac{x}{2} + \frac{\sin{\left(6 x \right)}}{12} \)

Problem 2.1258 · hard

Differentiate \( \displaystyle f(x) = - \frac{x}{2} + \frac{\sin{\left(6 x \right)}}{12} \).
  1. \[ \frac{d}{d x} \left(- \frac{x}{2} + \frac{\sin{\left(6 x \right)}}{12}\right) \]
    Start with the derivative of the function.✓ Proved
  2. \[ = \frac{d}{d x} \left(- \frac{x}{2}\right) + \frac{d}{d x} \frac{\sin{\left(6 x \right)}}{12} \]
    sumApply the sum rule.✓ Proved
  3. \[ = \frac{d}{d x} \left(- \frac{x}{2}\right) + \frac{\frac{d}{d x} \sin{\left(6 x \right)}}{12} \]
    constant-multipleFactor out the constant 1/12.✓ Proved
  4. \[ = \frac{\cos{\left(6 x \right)} \frac{d}{d x} 6 x}{12} + \frac{d}{d x} \left(- \frac{x}{2}\right) \]
    chainApply the chain rule to sin(6*x).✓ Proved
  5. \[ = \frac{\cos{\left(6 x \right)}}{2} + \frac{d}{d x} \left(- \frac{x}{2}\right) \]
    derivative algebra simplifyDifferentiate 6*x. Multiply the constants. Simplify the fraction.✓ Proved
  6. \[ = \frac{\cos{\left(6 x \right)}}{2} - \frac{1}{2} \]
    derivative simplifyDifferentiate the remaining term. Final simplified form.✓ Proved
Answer \( - \sin^{2}{\left(3 x \right)} \)

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
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 — The solution correctly applies differentiation rules step-by-step, adhering to the one-rule-per-step constraint. The final result is algebraically equivalent to the stated answer.
Every verdict on record (4)
  • qwen3.6:27b-mlx: pass 2026-09-29 — The solution correctly applies differentiation rules step-by-step, adhering to the one-rule-per-step constraint. The final result is algebraically equivalent to the stated answer.
  • gpt-oss:20b: pass 2026-09-29
  • qwen3.6:27b-mlx: fail (error) 2026-09-29 — The final result -1/2 + cos(6*x)/2 is not equal to the stated answer -sin(3*x)**2. While -sin^2(3x) = -1/2 + 1/2*cos(6x) is a valid identity, the solution steps stop at the cosine form and do not perform the algebraic rewrite to match the stated answer, nor does it claim the cosine form is the final answer. The solution fails to produce the stated answer.
  • gpt-oss:20b: pass 2026-09-29

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 2026-09-29 with SymPy 1.14.0.