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Derivative of \( \displaystyle \ln{\left(- \cot{\left(x \right)} + \csc{\left(x \right)} \right)} \)

Problem 2.9 · hard Beautiful

Differentiate \( \displaystyle f(x) = \ln{\left(- \cot{\left(x \right)} + \csc{\left(x \right)} \right)} \).
  1. \[ \frac{d}{d x} \ln{\left(- \cot{\left(x \right)} + \csc{\left(x \right)} \right)} \]
    derivativeStart with the derivative of the function.✓ Proved
  2. \[ = \frac{\frac{d}{d x} \left(- \cot{\left(x \right)} + \csc{\left(x \right)}\right)}{- \cot{\left(x \right)} + \csc{\left(x \right)}} \]
    chainApply the chain rule for the logarithm.✓ Proved
  3. \[ = \frac{- \frac{d}{d x} \cot{\left(x \right)} + \frac{d}{d x} \csc{\left(x \right)}}{- \cot{\left(x \right)} + \csc{\left(x \right)}} \]
    sumDistribute the derivative over the sum.✓ Proved
  4. \[ = \frac{- \cot{\left(x \right)} \csc{\left(x \right)} + \csc^{2}{\left(x \right)}}{- \cot{\left(x \right)} + \csc{\left(x \right)}} \]
    trig algebraApply the derivatives of cot(x) and csc(x). Simplify the signs inside the parentheses.✓ Proved
  5. \[ = \csc{\left(x \right)} \]
    algebra simplifyFactor out csc(x) from the numerator. Cancel the common term in the numerator and denominator.✓ Proved
Answer \( \csc{\left(x \right)} \)
Mind the domain. The answer is also defined at points where f(x) is not. Substituting there gives a number that is not a slope of f.

✓ 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
log is undefined for non-positive arguments
csc has poles at multiples of pi
cot has poles at multiples of pi
undefined where -cot(x) + csc(x) = 0
3✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
csc has poles at multiples of pi
cot has poles at multiples of pi
undefined where -cot(x) + csc(x) = 0
4✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
csc has poles at multiples of pi
cot has poles at multiples of pi
undefined where -cot(x) + csc(x) = 0
5✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
csc has poles at multiples of pi
cot has poles at multiples of pi
undefined where -cot(x) + csc(x) = 0
6✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
csc has poles at multiples of pi
cot has poles at multiples of pi
undefined where -cot(x) + csc(x) = 0
7✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
csc has poles at multiples of pi
answer✓ Provedsympy 1.14.0final line against the stated answer: simplify(a - b) reduced to 0
csc has poles at multiples of pi
answer, a second way✓ Provedsympy 1.14.0SymPy differentiated f directly and got the stated answer

Reviewers

  • deepseek-r1:70b: pass
  • gpt-oss:20b: pass
  • qwen3.6:27b-mlx: pass
Every verdict on record (11)
  • qwen3.6:27b-mlx: pass 2026-09-20
  • gpt-oss:20b: pass 2026-09-20
  • qwen3.6:27b-mlx: pass 2026-09-20
  • 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
  • deepseek-r1:70b: pass 2026-09-16

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.