Derivative of \( \displaystyle - x + \ln{\left(\frac{\sqrt{x^{2} - 1}}{\sqrt{1 - x^{2}}} \right)} \)
Problem 2.533 · hard Beautiful
Differentiate \( \displaystyle f(x) = - x + \ln{\left(\frac{\sqrt{x^{2} - 1}}{\sqrt{1 - x^{2}}} \right)} \).
- \[ \frac{d}{d x} \left(- x + \ln{\left(\frac{\sqrt{x^{2} - 1}}{\sqrt{1 - x^{2}}} \right)}\right) \]derivativeStart with the derivative of the function.✓ Proved
- \[ = \frac{d}{d x} \left(- x\right) + \frac{d}{d x} \ln{\left(\frac{\sqrt{x^{2} - 1}}{\sqrt{1 - x^{2}}} \right)} \]sum algebraApply the sum rule. Rewrite the quotient as a product using exponents.✓ Proved
- \[ = \frac{d}{d x} \left(- x\right) + \frac{d}{d x} \frac{\sqrt{x^{2} - 1}}{\sqrt{1 - x^{2}}} \]rewrite algebra algebraRewrite the log argument using the exponential identity. Apply the logarithm product rule. Apply the power rule for logarithms.✓ Proved
- \[ = \frac{d}{d x} \left(- x\right) + \frac{\sqrt{x^{2} - 1} \frac{d}{d x} \left(- \frac{\ln{\left(1 - x^{2} \right)}}{2} + \frac{\ln{\left(x^{2} - 1 \right)}}{2}\right)}{\sqrt{1 - x^{2}}} \]chainApply the chain rule.✓ Proved
- \[ = \frac{d}{d x} \left(- x\right) + \frac{\sqrt{x^{2} - 1} \left(- \frac{\frac{d}{d x} \ln{\left(1 - x^{2} \right)}}{2} + \frac{\frac{d}{d x} \ln{\left(x^{2} - 1 \right)}}{2}\right)}{\sqrt{1 - x^{2}}} \]constant-multipleDistribute the derivative across the subtraction.✓ Proved
- \[ = \frac{d}{d x} \left(- x\right) + \frac{\sqrt{x^{2} - 1} \left(\frac{x}{x^{2} - 1} + \frac{x}{1 - x^{2}}\right)}{\sqrt{1 - x^{2}}} \]chain algebraApply the chain rule to the logarithmic terms. Simplify the fractions.✓ Proved
- \[ = \frac{d}{d x} \left(- x\right) \]algebra algebraRewrite 1/(1 - x**2) as -1/(x**2 - 1). Combine the terms in the parentheses.✓ Proved
- \[ = -1 \]algebra simplifyEvaluate the derivative of -x and the zero term. Final simplification.✓ Proved
Answer \( -1 \)
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
| Line | Status | Checked by | Detail |
|---|---|---|---|
| 1 | ✓ Proved | sympy 1.14.0 | line 1 is the problem as stated |
| 2 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 log is undefined for non-positive arguments undefined where 1 - x**2 = 0 |
| 3 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 log is undefined for non-positive arguments undefined where 1 - x**2 = 0 |
| 4 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 log is undefined for non-positive arguments undefined where 1 - x**2 = 0 |
| 5 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 undefined where 1 - x**2 = 0 |
| 6 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 undefined where 1 - x**2 = 0 |
| 7 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 undefined where 1 - x**2 = 0 log is undefined for non-positive arguments |
| 8 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 log is undefined for non-positive arguments undefined where 1 - x**2 = 0 |
| 9 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 log is undefined for non-positive arguments undefined where 1 - x**2 = 0 undefined where x**2 - 1 = 0 |
| 10 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 undefined where x**2 - 1 = 0 undefined where 1 - x**2 = 0 |
| 11 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 undefined where x**2 - 1 = 0 undefined where 1 - x**2 = 0 |
| 12 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 |
| 13 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 |
| 14 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 |
| answer | ✓ Proved | sympy 1.14.0 | final line against the stated answer: simplify(a - b) reduced to 0 |
| answer, a second way | ✓ Proved | sympy 1.14.0 | SymPy differentiated f directly and got the stated answer |
Reviewers
gpt-oss:20b: fail (error) — Step 4 replaces “log(z)” with “exp(log(z))”, which is not an equivalent expression. This applies two incorrect transformations in one step and violates the rule that each step must change only one thing. The subsequent steps depend on this incorrect rewrite, so the solution is mathematically invalid.qwen3.6:27b-mlx: pass — The solution correctly applies the rules from the fixed vocabulary. Each step changes only one aspect of the expression or applies a single differentiation rule, 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 rules from the fixed vocabulary. Each step changes only one aspect of the expression or applies a single differentiation rule, and the labels accurately reflect the operations performed.gpt-oss:20b: fail (error) 2026-09-21 — Step 4 replaces “log(z)” with “exp(log(z))”, which is not an equivalent expression. This applies two incorrect transformations in one step and violates the rule that each step must change only one thing. The subsequent steps depend on this incorrect rewrite, so the solution is mathematically invalid.qwen3.6:27b-mlx: pass 2026-09-20 — The solution correctly applies differentiation rules and algebraic simplifications. Each step adheres to the single-change constraint, and the labels accurately reflect the operations performed.gpt-oss:20b: pass 2026-09-20qwen3.6:27b-mlx: pass 2026-09-20 — The solution correctly applies the sum rule, algebraic rewrites of the logarithm, and the chain rule. Each step isolates a single transformation, and the labels accurately reflect the operations performed.gpt-oss:20b: fail (error) 2026-09-20 — Step 4 replaces “log(A)” with “exp(log(A))”, changing the function and violating the derivative rule. Subsequent steps (5–7) apply product and logarithm rules inside the exponential, which is not a valid transformation. These steps apply multiple incorrect rules at once and alter the expression, so the solution is mathematically invalid.
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.