Limit of \( \displaystyle \frac{\sqrt{2} \sqrt{x} - 1}{2 x - 1} \) as \( x \to \frac{1}{2} \)
Problem 1.224 · medium
Evaluate \( \displaystyle \lim_{x \to \frac{1}{2}} \frac{\sqrt{2} \sqrt{x} - 1}{2 x - 1} \).
- \[ \lim_{x \to \frac{1}{2}^+}\left(\frac{\sqrt{2} \sqrt{x} - 1}{2 x - 1}\right) \]limitStart with the limit of the original function.✓ Proved
- \[ = \lim_{x \to \frac{1}{2}^+}\left(\sqrt{2} \sqrt{x} - 1\right) \left(\lim_{x \to \frac{1}{2}^+}\left(2 x - 1\right)\right)^{-1} \]limit-lawCheck the limit of the numerator and denominator separately.Not checked
- \[ = 1 \]limitEvaluate the limits of the numerator and denominator.Not checked
- \[ = \lim_{x \to \frac{1}{2}^+} \text{NaN} \]simplifyThe limit results in an indeterminate form.Not checked
- \[ = \lim_{x \to \frac{1}{2}^+}\left(\frac{\frac{d}{d x} \left(\sqrt{2} \sqrt{x} - 1\right)}{\frac{d}{d x} \left(2 x - 1\right)}\right) \]lhopitalApply L'Hopital's rule.Not checked
- \[ = \lim_{x \to \frac{1}{2}^+}\left(\frac{\sqrt{2}}{4 \sqrt{x}}\right) \]simplify algebraCompute the derivatives. Simplify the fraction.✓ Proved
- \[ = \frac{1}{2} \]limit simplify algebra simplify simplifyEvaluate the limit by substituting x = 1/2. Simplify the denominator. Multiply the numerator and denominator by sqrt(2). Simplify the expression. Final answer.✓ Proved
Answer \( \frac{1}{2} \)
Lines: 9 proved, 4 not checked. 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 | Not checked | — | simplify left nan; no point in the sample was defined on both lines undefined where 2*x - 1 = 0 undefined where Limit(2*x - 1, x, 1/2, dir='+') = 0 |
| 3 | Not checked | — | simplify left nan; no point in the sample was defined on both lines undefined where Limit(2*x - 1, x, 1/2, dir='+') = 0 |
| 4 | Not checked | — | simplify left nan; no point in the sample was defined on both lines |
| 5 | Not checked | — | simplify left nan; no point in the sample was defined on both lines undefined where Derivative(2*x - 1, x) = 0 |
| 6 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 undefined where Derivative(2*x - 1, x) = 0 undefined where x = 0 |
| 7 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 undefined where x = 0 |
| 8 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 undefined where x = 0 |
| 9 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 |
| 10 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 |
| 11 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 |
| 12 | ✓ 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: fail (error) — Step 3 incorrectly applies the limit operator to constants (e.g., Limit(2*(1/2) - 1, x, 1/2) should just be 0, not a limit expression). Step 4 is mathematically nonsensical as it claims the limit of a constant 0/0 is 0/0, rather than identifying the form. Step 6 labels the computation of derivatives as 'simplify', which is incorrect; it should be 'derivative' or 'algebra' depending on interpretation, but 'simplify' usually implies reducing an existing expression, not performing differentiation.
Every verdict on record (4)
qwen3.6:27b-mlx: fail (error) 2026-10-05 — Step 3 incorrectly applies the limit operator to constants (e.g., Limit(2*(1/2) - 1, x, 1/2) should just be 0, not a limit expression). Step 4 is mathematically nonsensical as it claims the limit of a constant 0/0 is 0/0, rather than identifying the form. Step 6 labels the computation of derivatives as 'simplify', which is incorrect; it should be 'derivative' or 'algebra' depending on interpretation, but 'simplify' usually implies reducing an existing expression, not performing differentiation.gpt-oss:20b: pass 2026-10-05qwen3.6:27b-mlx: pass 2026-10-05 — The solution correctly identifies the indeterminate form, applies L'Hopital's rule with valid derivatives, and simplifies the resulting expression to the correct limit. Each step adheres to the single-rule constraint and uses valid labels from the fixed vocabulary.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.