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 \( \displaystyle \lim_{x \to \frac{2}{3}} \frac{- 15 x + \left(3 x + 1\right)^{2} + 1}{3 x - 2} \).
- \[ \lim_{x \to \frac{2}{3}^+}\left(\frac{- 15 x + \left(3 x + 1\right)^{2} + 1}{3 x - 2}\right) \]limitStart with the limit of the given function.✓ Proved
- \[ = \lim_{x \to \frac{2}{3}^+}\left(\frac{9 x^{2} - 9 x + 2}{3 x - 2}\right) \]simplifyExpand and simplify the numerator.✓ Proved
- \[ = \lim_{x \to \frac{2}{3}^+}\left(3 x - 1\right) \]factor cancelFactor the numerator to reveal the common factor. Cancel the common factor (3*x - 2).✓ Proved
- \[ = 1 \]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
| 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 3*x - 2 = 0 |
| 3 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 undefined where 3*x - 2 = 0 |
| 4 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 |
| 5 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 |
| 6 | ✓ 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: passqwen3.6:27b-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 2026-10-10qwen3.6:27b-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 2026-10-10gpt-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.