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Limit of \( \displaystyle \frac{\sqrt{\left(3 x - 1\right)^{2} + 1}}{3 x - 1} \) as \( x \to \infty \)

Problem 1.244 · medium

Evaluate \( \displaystyle \lim_{x \to \infty} \frac{\sqrt{\left(3 x - 1\right)^{2} + 1}}{3 x - 1} \).
  1. \[ \lim_{x \to \infty}\left(\frac{\sqrt{\left(3 x - 1\right)^{2} + 1}}{3 x - 1}\right) \]
    limitEvaluate the limit as x approaches infinity.✓ Proved
  2. \[ = \lim_{x \to \infty}\left(\frac{\sqrt{1 + \frac{1}{\left(3 x - 1\right)^{2}}} \left|{3 x - 1}\right|}{3 x - 1}\right) \]
    algebra algebra simplifyFactor out (3*x - 1)**2 from the radicand. Use the property sqrt(a*b) = sqrt(a)*sqrt(b). Simplify the square root of the squared term.✓ Proved
  3. \[ = \lim_{x \to \infty} \sqrt{1 + \frac{1}{\left(3 x - 1\right)^{2}}} \]
    simplifySince x approaches infinity, 3*x - 1 is positive, so abs(3*x - 1)/(3*x - 1) = 1.✓ Proved
  4. \[ = \lim_{x \to \infty} 1 \]
    limit-lawThe term 1/(3*x - 1)**2 approaches 0 as x approaches infinity.✓ Proved
  5. \[ = 1 \]
    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
LineStatusChecked byDetail
1✓ Provedsympy 1.14.0line 1 is the problem as stated
2✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
undefined where 3*x - 1 = 0
3✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
undefined where 3*x - 1 = 0
4✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
undefined where 3*x - 1 = 0
5✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
undefined where 3*x - 1 = 0
6✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
undefined where 3*x - 1 = 0
7✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
answer✓ Provedsympy 1.14.0final line against the stated answer: simplify(a - b) reduced to 0
answer, a second way✓ Provedsympy 1.14.0SymPy took the limit from both sides and got the stated value

Reviewers

  • gpt-oss:20b: pass
  • qwen3.6:27b-mlx: pass — The solution correctly handles the absolute value arising from the square root of a squared term and applies limit laws appropriately. Each step changes only one aspect of the expression and uses valid labels from the vocabulary.
Every verdict on record (4)
  • qwen3.6:27b-mlx: pass 2026-10-05 — The solution correctly handles the absolute value arising from the square root of a squared term and applies limit laws appropriately. Each step changes only one aspect of the expression and uses valid labels from the vocabulary.
  • gpt-oss:20b: pass 2026-10-05
  • qwen3.6:27b-mlx: pass 2026-10-05
  • 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.