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Limit of \( \displaystyle \frac{8 x^{3} - 1}{4 x^{2} - 1} \) as \( x \to \frac{1}{2} \)

Problem 1.133 · medium

Evaluate \( \displaystyle \lim_{x \to \frac{1}{2}} \frac{8 x^{3} - 1}{4 x^{2} - 1} \).
  1. \[ \lim_{x \to \frac{1}{2}^+}\left(\frac{8 x^{3} - 1}{4 x^{2} - 1}\right) \]
    limitIdentify the limit to be evaluated.✓ Proved
  2. \[ = \lim_{x \to \frac{1}{2}^+}\left(\frac{4 x^{2} + 2 x + 1}{2 x + 1}\right) \]
    factor cancelFactor the numerator and denominator. Cancel the common factor (2*x - 1).✓ Proved
  3. \[ = \lim_{x \to \frac{1}{2}^+}\left(4 x^{2} + 2 x + 1\right) \left(\lim_{x \to \frac{1}{2}^+}\left(2 x + 1\right)\right)^{-1} \]
    limit-lawApply the quotient rule for limits.✓ Proved
  4. \[ = \frac{3}{2} \]
    limit simplifyEvaluate the limits of the numerator and denominator. Simplify the resulting numerical expression.✓ Proved
Answer \( \frac{3}{2} \)

✓ 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 4*x**2 - 1 = 0
undefined where 2*x + 1 = 0
3✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
undefined where 2*x + 1 = 0
4✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
undefined where 2*x + 1 = 0
undefined where Limit(2*x + 1, x, 1/2, dir='+') = 0
5✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
undefined where Limit(2*x + 1, x, 1/2, 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)
  • qwen3.6:27b-mlx: pass 2026-10-03
  • gpt-oss:20b: pass 2026-10-03
  • qwen3.6:27b-mlx: pass 2026-10-03
  • 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.