Limit of \( \displaystyle \frac{x}{\sqrt{\left(x - 1\right)^{2} + 4}} \) as \( x \to \infty \)
Problem 1.124 · medium
Evaluate \( \displaystyle \lim_{x \to \infty} \frac{x}{\sqrt{\left(x - 1\right)^{2} + 4}} \).
- \[ \lim_{x \to \infty}\left(\frac{x}{\sqrt{\left(x - 1\right)^{2} + 4}}\right) \]limitStart with the given limit.✓ Proved
- \[ = \lim_{x \to \infty}\left(\frac{x}{\sqrt{x^{2} - 2 x + 5}}\right) \]algebra simplifyExpand the squared term inside the square root. Combine the constant terms.✓ Proved
- \[ = \lim_{x \to \infty}\left(\frac{x}{\sqrt{1 - \frac{2}{x} + \frac{5}{x^{2}}} \left|{x}\right|}\right) \]rewriteFactor out x**2 from the expression inside the square root.✓ Proved
- \[ = \lim_{x \to \infty} \frac{1}{\sqrt{1 - \frac{2}{x} + \frac{5}{x^{2}}}} \]algebra simplifyTake x out of the square root, noting that x is positive as x approaches infinity. Cancel the common factor of x in the numerator and denominator.✓ Proved
- \[ = \lim_{x \to \infty} 1 \]limit-lawApply the limit to each term inside the expression.✓ Proved
- \[ = 1 \]limitEvaluate the final expression.✓ Proved
Answer \( 1 \)
✓ 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 + 4 = 0 undefined where x**2 - 2*x + 5 = 0 |
| 3 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 undefined where x**2 - 2*x + 5 = 0 |
| 4 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 undefined where x**2 - 2*x + 5 = 0 undefined where Abs(x) = 0 undefined where 1 - 2/x + 5/x**2 = 0 undefined where x = 0 |
| 5 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 undefined where Abs(x) = 0 undefined where 1 - 2/x + 5/x**2 = 0 undefined where x = 0 |
| 6 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 undefined where 1 - 2/x + 5/x**2 = 0 undefined where x = 0 |
| 7 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 undefined where 1 - 2/x + 5/x**2 = 0 undefined where x = 0 |
| 8 | ✓ 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 5 applies two transformations at once (taking the square root of a product and canceling the common factor of x). Each step should change only one thing, so this step should be split into two separate steps with appropriate labels.qwen3.6:27b-mlx: pass — The solution correctly applies algebraic manipulations and limit laws to evaluate the limit. 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 algebraic manipulations and limit laws to evaluate the limit. Each step changes only one aspect of the expression and uses valid labels from the fixed vocabulary.gpt-oss:20b: fail (style) 2026-10-03 — Step 5 applies two transformations at once (taking the square root of a product and canceling the common factor of x). Each step should change only one thing, so this step should be split into two separate steps with appropriate labels.qwen3.6:27b-mlx: pass 2026-10-03 — The solution correctly applies algebraic manipulation and limit laws to evaluate the limit. Each step changes only one aspect of the expression 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.