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Derivative of \( \displaystyle \sin{\left(2 x + 1 \right)} \)

Problem 2.172 · medium

Differentiate \( \displaystyle f(x) = \sin{\left(2 x + 1 \right)} \).
  1. \[ \frac{d}{d x} \sin{\left(2 x + 1 \right)} \]
    derivativeStart with the derivative of the function.✓ Proved
  2. \[ = \cos{\left(2 x + 1 \right)} \frac{d}{d x} \left(2 x + 1\right) \]
    chainApply the chain rule.✓ Proved
  3. \[ = \left(\frac{d}{d x} 1 + \frac{d}{d x} 2 x\right) \cos{\left(2 x + 1 \right)} \]
    sumDifferentiate the sum inside the parentheses.✓ Proved
  4. \[ = \left(\frac{d}{d x} 1 + 2\right) \cos{\left(2 x + 1 \right)} \]
    derivativeDifferentiate 2*x.✓ Proved
  5. \[ = 2 \cos{\left(2 x + 1 \right)} \]
    derivative algebraDifferentiate the constant 1. Simplify the expression.✓ Proved
Answer \( 2 \cos{\left(2 x + 1 \right)} \)

✓ 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
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: pass
Every verdict on record (15)
  • qwen3.6:27b-mlx: pass 2026-09-20
  • gpt-oss:20b: pass 2026-09-20
  • qwen3.6:27b-mlx: pass 2026-09-20 — The solution correctly applies the chain rule, sum rule, and derivative rules in a step-by-step manner. Each step changes only one aspect of the expression and uses valid labels from the fixed vocabulary.
  • 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: pass 2026-09-18 — The solution correctly applies the chain rule, sum rule, and derivative rules in a step-by-step manner, adhering to the one-change-per-step constraint.
  • deepseek-r1:70b: pass 2026-09-18
  • gpt-oss:20b: pass 2026-09-18
  • gpt-oss:20b: pass 2026-09-17
  • 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.