∫Calc Practice
Home›Calculus 1›Quotient rule›Problem 2.409

Derivative of \( \displaystyle \frac{\cos{\left(x \right)}}{x} \)

Problem 2.409 · hard

Differentiate \( \displaystyle f(x) = \frac{\cos{\left(x \right)}}{x} \).
  1. \[ \frac{d}{d x} \frac{\cos{\left(x \right)}}{x} \]
    derivative algebraStart with the derivative of the function. Rewrite the quotient as a product.✓ Proved
  2. \[ = \cos{\left(x \right)} \frac{d}{d x} \frac{1}{x} + \frac{\frac{d}{d x} \cos{\left(x \right)}}{x} \]
    productApply the product rule.✓ Proved
  3. \[ = \cos{\left(x \right)} \frac{d}{d x} \frac{1}{x} - \frac{\sin{\left(x \right)}}{x} \]
    trigDifferentiate cos(x).✓ Proved
  4. \[ = - \frac{\sin{\left(x \right)}}{x} - \frac{\cos{\left(x \right)}}{x^{2}} \]
    power algebraDifferentiate 1/x using the power rule. Simplify the terms.✓ Proved
  5. \[ = \frac{- x \sin{\left(x \right)} - \cos{\left(x \right)}}{x^{2}} \]
    simplifyCombine into a single fraction.✓ Proved
Answer \( - \frac{\sin{\left(x \right)} + \frac{\cos{\left(x \right)}}{x}}{x} \)

✓ 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
undefined where x = 0
3✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
undefined where x = 0
4✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
undefined where x = 0
5✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
undefined where x = 0
6✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
undefined where x = 0
7✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
undefined where x = 0
answer✓ Provedsympy 1.14.0final line against the stated answer: simplify(a - b) reduced to 0
undefined where x = 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 the product rule and standard differentiation rules. Each step isolates a single transformation, and the labels accurately reflect the operations performed.
Every verdict on record (6)
  • qwen3.6:27b-mlx: pass 2026-09-21 — The solution correctly applies the product rule and standard differentiation rules. Each step isolates a single transformation, and the labels accurately reflect the operations performed.
  • gpt-oss:20b: pass 2026-09-21
  • qwen3.6:27b-mlx: pass 2026-09-20 — The solution correctly applies the product rule and standard differentiation rules. Each step isolates a single transformation, and the labels accurately describe the operations performed.
  • gpt-oss:20b: pass 2026-09-20
  • qwen3.6:27b-mlx: pass 2026-09-20
  • gpt-oss:20b: pass 2026-09-20

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.