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Limit of \( \displaystyle \frac{36 x^{2} - 1}{18 x^{2} + 3 x} \) as \( x \to \infty \)

Problem 1.304 · medium

Evaluate \( \displaystyle \lim_{x \to \infty} \frac{36 x^{2} - 1}{18 x^{2} + 3 x} \).
  1. \[ \lim_{x \to \infty}\left(\frac{36 x^{2} - 1}{18 x^{2} + 3 x}\right) \]
    limit algebraStart with the limit of the given function as x approaches infinity. Divide the numerator and denominator by x**2.✓ Proved
  2. \[ = \lim_{x \to \infty}\left(\frac{36 - \frac{1}{x^{2}}}{18 + \frac{3}{x}}\right) \]
    simplifySimplify the terms inside the limit.✓ Proved
  3. \[ = \lim_{x \to \infty}\left(36 - \frac{1}{x^{2}}\right) \left(\lim_{x \to \infty}\left(18 + \frac{3}{x}\right)\right)^{-1} \]
    limit-lawApply the quotient rule for limits.✓ Proved
  4. \[ = 2 \]
    limit simplifyEvaluate the limits of the numerator and denominator separately. Simplify the resulting fraction.✓ Proved
Answer \( 2 \)

✓ 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
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 18*x**2 + 3*x = 0
3✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
undefined where 18*x**2 + 3*x = 0
undefined where x = 0
undefined where 18 + 3/x = 0
4✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
undefined where x = 0
undefined where 18 + 3/x = 0
undefined where Limit(18 + 3/x, x, oo, dir='-') = 0
5✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
undefined where x = 0
undefined where Limit(18 + 3/x, x, oo, dir='-') = 0
6✓ 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
Every verdict on record (4)
  • gpt-oss:20b: pass 2026-10-06
  • qwen3.6:27b-mlx: pass 2026-10-06
  • qwen3.6:27b-mlx: fail (style) 2026-10-06 — Step 5 applies the limit evaluation to both the numerator and denominator simultaneously, violating the one-change-per-step rule. It should be split into two steps, one for the numerator and one for the denominator.
  • gpt-oss:20b: pass 2026-10-06

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 2026-10-06 with SymPy 1.14.0.