Limit of \( \displaystyle \frac{- 2 x + \left(2 x - 1\right)^{2} + 1}{\left(2 x - 1\right)^{2} - 1} \) as \( x \to 1 \)
Problem 1.371 · hard
Evaluate \( \displaystyle \lim_{x \to 1} \frac{- 2 x + \left(2 x - 1\right)^{2} + 1}{\left(2 x - 1\right)^{2} - 1} \).
- \[ \lim_{x \to 1^+}\left(\frac{- 2 x + \left(2 x - 1\right)^{2} + 1}{\left(2 x - 1\right)^{2} - 1}\right) \]limitEvaluate the limit of the given function at x = 1.✓ Proved
- \[ = \lim_{x \to 1^+}\left(\frac{\frac{d}{d x} \left(- 2 x + \left(2 x - 1\right)^{2} + 1\right)}{\frac{d}{d x} \left(\left(2 x - 1\right)^{2} - 1\right)}\right) \]lhopitalApply L'Hopital's Rule because the limit is in the form 0/0.✓ Proved
- \[ = \lim_{x \to 1^+}\left(\frac{8 x - 6}{8 x - 4}\right) \]simplify simplifyCompute the derivatives of the numerator and denominator. Simplify the expression by distributing the constants.✓ Proved
- \[ = \lim_{x \to 1^+}\left(1 - \frac{2}{8 x - 4}\right) \]algebraSplit the fraction into two parts.✓ Proved
- \[ = \lim_{x \to 1^+}\left(1 - \frac{1}{4 x - 2}\right) \]simplifySimplify the fraction coefficient.✓ Proved
- \[ = \lim_{x \to 1^+} \frac{1}{2} \]substitution simplifySubstitute x = 1 into the expression. Evaluate the denominator.✓ Proved
- \[ = \frac{1}{2} \]limitFinal result.✓ 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 (2*x - 1)**2 - 1 = 0 undefined where Derivative((2*x - 1)**2 - 1, x) = 0 |
| 3 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 undefined where Derivative((2*x - 1)**2 - 1, x) = 0 undefined where 8*x - 4 = 0 |
| 4 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 undefined where 8*x - 4 = 0 |
| 5 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 undefined where 8*x - 4 = 0 |
| 6 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 undefined where 8*x - 4 = 0 undefined where 4*x - 2 = 0 |
| 7 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 undefined where 4*x - 2 = 0 |
| 8 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 |
| 9 | ✓ 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: fail (style) — Step 3 is labeled "simplify" but it actually applies the derivative rule to both the numerator and the denominator. The label should be "derivative" (or a combined rule if allowed), not "simplify".qwen3.6:27b-mlx: pass
Every verdict on record (4)
gpt-oss:20b: fail (style) 2026-10-07 — Step 3 is labeled "simplify" but it actually applies the derivative rule to both the numerator and the denominator. The label should be "derivative" (or a combined rule if allowed), not "simplify".qwen3.6:27b-mlx: pass 2026-10-07gpt-oss:20b: pass 2026-10-07qwen3.6:27b-mlx: pass 2026-10-07 — The solution correctly applies L'Hopital's Rule and performs valid algebraic simplifications. Each step changes only one aspect of the expression and uses an acceptable label from the fixed vocabulary.
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 2026-10-07 with SymPy 1.14.0.