Limit of \( \displaystyle \frac{18 x^{2} - 9 x - 2}{3 x - 2} \) as \( x \to \frac{2}{3} \)
Problem 1.43 · medium
Evaluate \( \displaystyle \lim_{x \to \frac{2}{3}} \frac{18 x^{2} - 9 x - 2}{3 x - 2} \).
- \[ \lim_{x \to \frac{2}{3}^+}\left(\frac{18 x^{2} - 9 x - 2}{3 x - 2}\right) \]limitEvaluate the limit of the given function at x = 2/3.✓ Proved
- \[ = \lim_{x \to \frac{2}{3}^+} \text{NaN} \]simplifyNotice that the numerator and denominator both evaluate to zero at x = 2/3.Reviewed
- \[ = \lim_{x \to \frac{2}{3}^+}\left(\frac{\frac{d}{d x} \left(18 x^{2} - 9 x - 2\right)}{\frac{d}{d x} \left(3 x - 2\right)}\right) \]lhopitalApply L'Hopital's Rule because the limit is in indeterminate form 0/0.Reviewed
- \[ = \lim_{x \to \frac{2}{3}^+}\left(12 x - 3\right) \]simplify algebraCompute the derivatives of the numerator and the denominator. Simplify the fraction by dividing both terms in the numerator by 3.✓ Proved
- \[ = 5 \]limit algebra simplifySubstitute x = 2/3 into the simplified expression. Perform the multiplication. Calculate the final value.✓ Proved
Answer \( 5 \)
Lines: 7 proved, 2 reviewed. 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 | Reviewed | reviewers: gpt-oss:20b, qwen3.6:27b-mlx | simplify left nan; no point in the sample was defined on both lines undefined where 3*x - 2 = 0 |
| 3 | Reviewed | reviewers: gpt-oss:20b, qwen3.6:27b-mlx | simplify left nan; no point in the sample was defined on both lines undefined where Derivative(3*x - 2, x) = 0 |
| 4 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 undefined where Derivative(3*x - 2, x) = 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 |
| 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
Every verdict on record (4)
qwen3.6:27b-mlx: pass 2026-09-29gpt-oss:20b: pass 2026-09-29qwen3.6:27b-mlx: pass 2026-09-29gpt-oss:20b: pass 2026-09-29
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 2026-09-29 with SymPy 1.14.0.