Limit of \( \displaystyle \frac{- x + \left(x - 1\right)^{2} + 1}{\left(x - 1\right)^{2} - 1} \) as \( x \to 2 \)
Problem 1.235 · medium
Evaluate \( \displaystyle \lim_{x \to 2} \frac{- x + \left(x - 1\right)^{2} + 1}{\left(x - 1\right)^{2} - 1} \).
- \[ \lim_{x \to 2^+}\left(\frac{- x + \left(x - 1\right)^{2} + 1}{\left(x - 1\right)^{2} - 1}\right) \]limitStart with the limit of the given function.✓ Proved
- \[ = \lim_{x \to 2^+}\left(\frac{x^{2} - 3 x + 2}{x^{2} - 2 x}\right) \]simplifyExpand the numerator and denominator.✓ Proved
- \[ = \lim_{x \to 2^+}\left(\frac{x - 1}{x}\right) \]factor cancelFactor both the numerator and the denominator. Cancel the common factor (x - 2).✓ Proved
- \[ = \frac{1}{2} \]limitEvaluate the limit by substituting x = 2.✓ Proved
Answer \( \frac{1}{2} \)
✓ 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)**2 - 1 = 0 undefined where x**2 - 2*x = 0 |
| 3 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 undefined where x**2 - 2*x = 0 undefined where x = 0 |
| 4 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 undefined where x = 0 |
| 5 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 undefined where x = 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
Every verdict on record (4)
qwen3.6:27b-mlx: pass 2026-10-05gpt-oss:20b: pass 2026-10-05qwen3.6:27b-mlx: pass 2026-10-05 — The solution correctly expands, factors, cancels, and evaluates the limit. Each step applies a single rule from the allowed vocabulary and is algebraically sound.gpt-oss:20b: pass 2026-10-05
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 2026-10-05 with SymPy 1.14.0.