Limit of \( \displaystyle \frac{- 9 x + 2 \left(3 x + 1\right)^{2} - 5}{3 x - 1} \) as \( x \to \frac{1}{3} \)
Problem 1.372 · hard
Evaluate \( \displaystyle \lim_{x \to \frac{1}{3}} \frac{- 9 x + 2 \left(3 x + 1\right)^{2} - 5}{3 x - 1} \).
- \[ \lim_{x \to \frac{1}{3}^+}\left(\frac{- 9 x + 2 \left(3 x + 1\right)^{2} - 5}{3 x - 1}\right) \]limit algebraStart with the limit of the given function. Rearrange the terms in the numerator.✓ Proved
- \[ = \lim_{x \to \frac{1}{3}^+}\left(\frac{18 x^{2} + 3 x - 3}{3 x - 1}\right) \]simplify simplify simplify factorExpand the squared binomial. Distribute the 2. Combine like terms in the numerator. Factor out the constant 3.✓ Proved
- \[ = \lim_{x \to \frac{1}{3}^+}\left(\frac{\left(2 x + 1\right) \left(9 x - 3\right)}{3 x - 1}\right) \]factorFactor the quadratic expression in the numerator.✓ Proved
- \[ = \lim_{x \to \frac{1}{3}^+}\left(6 x + 3\right) \]cancelCancel the common factor (3*x - 1).✓ Proved
- \[ = 5 \]limit algebra algebra simplifyEvaluate the limit by substituting x = 1/3. Multiply 2 by 1/3. Add the terms in the parentheses. Final simplification.✓ Proved
Answer \( 5 \)
✓ 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 - 1 = 0 |
| 3 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 undefined where 3*x - 1 = 0 |
| 4 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 undefined where 3*x - 1 = 0 |
| 5 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 undefined where 3*x - 1 = 0 |
| 6 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 undefined where 3*x - 1 = 0 |
| 7 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 undefined where 3*x - 1 = 0 |
| 8 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 undefined where 3*x - 1 = 0 |
| 9 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 |
| 10 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 |
| 11 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 |
| 12 | ✓ 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 resolve the indeterminate form. Each step adheres to the single-rule constraint and uses valid labels from the fixed vocabulary.
Every verdict on record (4)
gpt-oss:20b: pass 2026-10-07qwen3.6:27b-mlx: pass 2026-10-07 — The solution correctly applies algebraic simplification, factoring, and cancellation to resolve the indeterminate form. Each step adheres to the single-rule constraint and uses valid labels from the fixed vocabulary.gpt-oss:20b: pass 2026-10-07qwen3.6:27b-mlx: pass 2026-10-07 — The solution correctly applies algebraic simplification, factoring, and cancellation to resolve the indeterminate form. Each step changes only one aspect of the expression and uses valid labels from the fixed vocabulary.
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 2026-10-07 with SymPy 1.14.0.