Limit of \( \displaystyle \frac{\left(3 x - 1\right)^{2} - 1}{3 x - 2} \) as \( x \to \frac{2}{3} \)
Problem 1.149 · medium
Evaluate \( \displaystyle \lim_{x \to \frac{2}{3}} \frac{\left(3 x - 1\right)^{2} - 1}{3 x - 2} \).
- \[ \lim_{x \to \frac{2}{3}^+}\left(\frac{\left(3 x - 1\right)^{2} - 1}{3 x - 2}\right) \]limit simplifyStart with the limit of the function as x approaches 2/3 from the right. The limit is the same from both sides since the function is continuous near 2/3 except at the point itself.✓ Proved
- \[ = \lim_{x \to \frac{2}{3}^+}\left(\frac{9 x^{2} - 6 x}{3 x - 2}\right) \]algebra simplifyExpand the squared term in the numerator. Simplify the numerator by subtracting the constants.✓ Proved
- \[ = \lim_{x \to \frac{2}{3}^+}\left(3 x\right) \]factor cancelFactor the numerator to reveal the common factor in the denominator. Cancel the common factor (3*x - 2) from the numerator and denominator.✓ Proved
- \[ = 2 \]limit simplifyEvaluate the remaining expression at x = 2/3. Final result.✓ 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
| 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 undefined where 3*x - 2 = 0 |
| 5 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 undefined where 3*x - 2 = 0 |
| 6 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 |
| 7 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 |
| 8 | ✓ 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 applies algebraic simplification, factoring, and cancellation to evaluate the limit. Each step changes only one aspect of the expression and uses appropriate labels from the fixed vocabulary.
Every verdict on record (4)
qwen3.6:27b-mlx: pass 2026-10-04 — The solution correctly applies algebraic simplification, factoring, and cancellation to evaluate the limit. Each step changes only one aspect of the expression and uses appropriate labels from the fixed vocabulary.gpt-oss:20b: pass 2026-10-04qwen3.6:27b-mlx: pass 2026-10-04 — The solution correctly applies algebraic simplification, factoring, and cancellation to evaluate the limit. Each step changes only one aspect of the expression and uses valid labels from the fixed vocabulary.gpt-oss:20b: pass 2026-10-04
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 2026-10-04 with SymPy 1.14.0.