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Derivative of \( \displaystyle \ln{\left(\frac{x}{\sqrt{1 - x^{2}}} \right)} \)

Problem 2.348 · hard Beautiful

Differentiate \( \displaystyle f(x) = \ln{\left(\frac{x}{\sqrt{1 - x^{2}}} \right)} \).
  1. \[ \frac{d}{d x} \ln{\left(\frac{x}{\sqrt{1 - x^{2}}} \right)} \]
    Start with the derivative of the function.✓ Proved
  2. \[ = \frac{d}{d x} \left(\ln{\left(x \right)} - \ln{\left(\sqrt{1 - x^{2}} \right)}\right) \]
    logarithmic algebraUse the property log(a/b) = log(a) - log(b). Rewrite the square root as a power.✓ Proved
  3. \[ = \frac{d}{d x} \left(\ln{\left(x \right)} - \frac{\ln{\left(1 - x^{2} \right)}}{2}\right) \]
    constant-multiplePull out the constant factor 1/2.✓ Proved
  4. \[ = \frac{d}{d x} \ln{\left(x \right)} - \frac{d}{d x} \frac{\ln{\left(1 - x^{2} \right)}}{2} \]
    sumApply the difference rule for derivatives.✓ Proved
  5. \[ = - \frac{d}{d x} \frac{\ln{\left(1 - x^{2} \right)}}{2} + \frac{1}{x} \]
    derivativeDifferentiate the first term.✓ Proved
  6. \[ = - \frac{\frac{d}{d x} \ln{\left(1 - x^{2} \right)}}{2} + \frac{1}{x} \]
    constant-multiplePull out the constant factor 1/2 from the second term.✓ Proved
  7. \[ = - \frac{\frac{d}{d x} \left(1 - x^{2}\right)}{2 \left(1 - x^{2}\right)} + \frac{1}{x} \]
    chainApply the chain rule to the logarithm.✓ Proved
  8. \[ = \frac{x}{1 - x^{2}} + \frac{1}{x} \]
    derivative algebraDifferentiate the inner function 1 - x**2. Simplify the signs and constants.✓ Proved
  9. \[ = \frac{1}{x \left(1 - x^{2}\right)} \]
    algebra simplifyFind a common denominator. Simplify the numerator.✓ Proved
Answer \( \frac{1}{- x^{3} + x} \)
Mind the domain. The answer is also defined on (-oo, -1) and (-1, 0) and (1, oo), 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
undefined where 1 - x**2 = 0
3✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
log is undefined for non-positive arguments
4✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
log is undefined for non-positive arguments
5✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
log is undefined for non-positive arguments
6✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
log is undefined for non-positive arguments
undefined where x = 0
7✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
log is undefined for non-positive arguments
undefined where x = 0
8✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
log is undefined for non-positive arguments
undefined where x = 0
undefined where 1 - x**2 = 0
9✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
undefined where 1 - x**2 = 0
undefined where x = 0
10✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
undefined where 1 - x**2 = 0
undefined where x = 0
11✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
undefined where 1 - x**2 = 0
undefined where x = 0
12✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
undefined where 1 - x**2 = 0
undefined where x = 0
answer✓ Provedsympy 1.14.0final line against the stated answer: simplify(a - b) reduced to 0
undefined where -x**3 + x = 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 — The solution correctly applies differentiation rules and algebraic simplifications. Each step changes only one aspect of the expression, and the labels accurately reflect the operations performed.
Every verdict on record (13)
  • qwen3.6:27b-mlx: pass 2026-09-20 — The solution correctly applies differentiation rules and algebraic simplifications. Each step changes only one aspect of the expression, and the labels accurately reflect the operations performed.
  • gpt-oss:20b: pass 2026-09-20
  • qwen3.6:27b-mlx: pass 2026-09-20 — The solution correctly applies differentiation rules and algebraic simplifications. Each step isolates a single transformation, and the labels accurately reflect the operations performed.
  • 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
  • deepseek-r1:70b: fail (style) 2026-09-18 — Step 1 lacks a rule label.
  • gpt-oss:20b: pass 2026-09-18

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.