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Limit of \( \displaystyle \frac{- 15 x + \left(3 x + 1\right)^{2} + 1}{3 x - 2} \) as \( x \to \frac{2}{3} \)

Problem 1.499 · medium

Evaluate \( \displaystyle \lim_{x \to \frac{2}{3}} \frac{- 15 x + \left(3 x + 1\right)^{2} + 1}{3 x - 2} \).
  1. \[ \lim_{x \to \frac{2}{3}^+}\left(\frac{- 15 x + \left(3 x + 1\right)^{2} + 1}{3 x - 2}\right) \]
    limitStart with the limit of the given function.✓ Proved
  2. \[ = \lim_{x \to \frac{2}{3}^+}\left(\frac{9 x^{2} - 9 x + 2}{3 x - 2}\right) \]
    simplifyExpand and simplify the numerator.✓ Proved
  3. \[ = \lim_{x \to \frac{2}{3}^+}\left(3 x - 1\right) \]
    factor cancelFactor the numerator to reveal the common factor. Cancel the common factor (3*x - 2).✓ Proved
  4. \[ = 1 \]
    substitution limitSubstitute x = 2/3 into the simplified expression. Evaluate the final value.✓ 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 - 2 = 0
3✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
undefined where 3*x - 2 = 0
4✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
5✓ Provedsympy 1.14.0simplify(a - b) reduced to 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 — The solution correctly expands, factors, and cancels the indeterminate form, then evaluates the limit via substitution. Each step applies a single rule and uses valid labels from the vocabulary.
Every verdict on record (4)
  • gpt-oss:20b: pass 2026-10-10
  • qwen3.6:27b-mlx: pass 2026-10-10 — The solution correctly expands, factors, and cancels the indeterminate form, then evaluates the limit via substitution. Each step applies a single rule and uses valid labels from the vocabulary.
  • qwen3.6:27b-mlx: pass 2026-10-10
  • gpt-oss:20b: pass 2026-10-10

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 2026-10-10 with SymPy 1.14.0.