∫Calc Practice

Limit of \( \displaystyle \frac{18 x^{2} - 9 x - 2}{3 x - 2} \) as \( x \to \frac{2}{3} \)

Problem 1.43 · medium

Evaluate \( \displaystyle \lim_{x \to \frac{2}{3}} \frac{18 x^{2} - 9 x - 2}{3 x - 2} \).
  1. \[ \lim_{x \to \frac{2}{3}^+}\left(\frac{18 x^{2} - 9 x - 2}{3 x - 2}\right) \]
    limitEvaluate the limit of the given function at x = 2/3.✓ Proved
  2. \[ = \lim_{x \to \frac{2}{3}^+} \text{NaN} \]
    simplifyNotice that the numerator and denominator both evaluate to zero at x = 2/3.Reviewed
  3. \[ = \lim_{x \to \frac{2}{3}^+}\left(\frac{\frac{d}{d x} \left(18 x^{2} - 9 x - 2\right)}{\frac{d}{d x} \left(3 x - 2\right)}\right) \]
    lhopitalApply L'Hopital's Rule because the limit is in indeterminate form 0/0.Reviewed
  4. \[ = \lim_{x \to \frac{2}{3}^+}\left(12 x - 3\right) \]
    simplify algebraCompute the derivatives of the numerator and the denominator. Simplify the fraction by dividing both terms in the numerator by 3.✓ Proved
  5. \[ = 5 \]
    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
LineStatusChecked byDetail
1✓ Provedsympy 1.14.0line 1 is the problem as stated
2Reviewedreviewers: gpt-oss:20b, qwen3.6:27b-mlxsimplify left nan; no point in the sample was defined on both lines
undefined where 3*x - 2 = 0
3Reviewedreviewers: gpt-oss:20b, qwen3.6:27b-mlxsimplify left nan; no point in the sample was defined on both lines
undefined where Derivative(3*x - 2, x) = 0
4✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
undefined where Derivative(3*x - 2, x) = 0
5✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
6✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
7✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
8✓ 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 2026-09-29
  • gpt-oss:20b: pass 2026-09-29
  • qwen3.6:27b-mlx: pass 2026-09-29
  • gpt-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.