Limit of \( \displaystyle \frac{1 - \cos{\left(x - 1 \right)}}{x - 1} \) as \( x \to 1 \)
Problem 1.103 · medium
Evaluate \( \displaystyle \lim_{x \to 1} \frac{1 - \cos{\left(x - 1 \right)}}{x - 1} \).
- \[ \lim_{x \to 1^+}\left(\frac{1 - \cos{\left(x - 1 \right)}}{x - 1}\right) \]limitStart with the limit of the original function.✓ Proved
- \[ = \lim_{x \to 1^+}\left(\frac{\frac{d}{d x} \left(1 - \cos{\left(x - 1 \right)}\right)}{\frac{d}{d x} \left(x - 1\right)}\right) \]lhopitalApply L'Hopital's rule since the limit is an indeterminate form 0/0.✓ Proved
- \[ = \lim_{x \to 1^+} \sin{\left(x - 1 \right)} \]simplify simplifyCompute the derivatives of the numerator and denominator. Simplify the expression.✓ Proved
- \[ = 0 \]limit simplifyEvaluate the limit by substituting x = 1. Final result.✓ Proved
Answer \( 0 \)
✓ 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
| 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 undefined where x - 1 = 0 undefined where Derivative(x - 1, x) = 0 |
| 3 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 undefined where Derivative(x - 1, x) = 0 |
| 4 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 |
| 5 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 |
| 6 | ✓ 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 took the limit from both sides and got the stated value |
Reviewers
gpt-oss:20b: passqwen3.6:27b-mlx: pass — The solution correctly applies L'Hopital's rule to resolve the 0/0 indeterminate form. Each step changes only one aspect of the expression and uses valid labels from the fixed vocabulary.
Every verdict on record (4)
qwen3.6:27b-mlx: pass 2026-10-03 — The solution correctly applies L'Hopital's rule to resolve the 0/0 indeterminate form. Each step changes only one aspect of the expression and uses valid labels from the fixed vocabulary.gpt-oss:20b: pass 2026-10-03qwen3.6:27b-mlx: pass 2026-10-03 — The solution correctly applies L'Hopital's rule to resolve the 0/0 indeterminate form. Each step changes only one aspect of the expression (applying the rule, computing derivatives, simplifying, or evaluating) and uses valid labels from the fixed vocabulary.gpt-oss:20b: pass 2026-10-03
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 2026-10-03 with SymPy 1.14.0.