Limit of \( \displaystyle \frac{- 6 x + 2 \left(2 x + 1\right)^{2} - 5}{2 x - 1} \) as \( x \to \frac{1}{2} \)
Problem 1.230 · hard
Evaluate \( \displaystyle \lim_{x \to \frac{1}{2}} \frac{- 6 x + 2 \left(2 x + 1\right)^{2} - 5}{2 x - 1} \).
- \[ \lim_{x \to \frac{1}{2}^+}\left(\frac{- 6 x + 2 \left(2 x + 1\right)^{2} - 5}{2 x - 1}\right) \]limitStart with the limit of the given function.✓ Proved
- \[ = \lim_{x \to \frac{1}{2}^+}\left(\frac{8 x^{2} + 2 x - 3}{2 x - 1}\right) \]simplifyExpand and simplify the numerator.✓ Proved
- \[ = \lim_{x \to \frac{1}{2}^+}\left(\frac{\frac{d}{d x} \left(8 x^{2} + 2 x - 3\right)}{\frac{d}{d x} \left(2 x - 1\right)}\right) \]lhopitalApply L'Hopital's rule since the limit is of the form 0/0.✓ Proved
- \[ = \lim_{x \to \frac{1}{2}^+}\left(8 x + 1\right) \]simplify simplifyCompute the derivatives. Simplify the resulting expression.✓ Proved
- \[ = 5 \]limitEvaluate the limit at x = 1/2.✓ 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 2*x - 1 = 0 |
| 3 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 undefined where 2*x - 1 = 0 undefined where Derivative(2*x - 1, x) = 0 |
| 4 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 undefined where Derivative(2*x - 1, 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 |
| 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 L'Hopital's rule after simplifying the numerator, and each step adheres to the single-rule constraint with appropriate labels.
Every verdict on record (4)
qwen3.6:27b-mlx: pass 2026-10-05 — The solution correctly applies L'Hopital's rule after simplifying the numerator, and each step adheres to the single-rule constraint with appropriate labels.gpt-oss:20b: pass 2026-10-05qwen3.6:27b-mlx: pass 2026-10-05 — The solution correctly expands the numerator, applies L'Hopital's rule to the 0/0 form, computes the derivatives, and evaluates the final limit. Each step applies a single rule and uses valid labels from the vocabulary.gpt-oss:20b: pass 2026-10-05
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 2026-10-05 with SymPy 1.14.0.