∫Calc Practice
Home›Calculus 1›Limits by factoring›Problem 1.230

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 \( \displaystyle \lim_{x \to \frac{1}{2}} \frac{- 6 x + 2 \left(2 x + 1\right)^{2} - 5}{2 x - 1} \).
  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
  2. \[ = \lim_{x \to \frac{1}{2}^+}\left(\frac{8 x^{2} + 2 x - 3}{2 x - 1}\right) \]
    simplifyExpand and simplify the numerator.✓ Proved
  3. \[ = \lim_{x \to \frac{1}{2}^+}\left(\frac{\frac{d}{d x} \left(8 x^{2} + 2 x - 3\right)}{\frac{d}{d x} \left(2 x - 1\right)}\right) \]
    lhopitalApply L'Hopital's rule since the limit is of the form 0/0.✓ Proved
  4. \[ = \lim_{x \to \frac{1}{2}^+}\left(8 x + 1\right) \]
    simplify simplifyCompute the derivatives. Simplify the resulting expression.✓ Proved
  5. \[ = 5 \]
    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
LineStatusChecked byDetail
1✓ Provedsympy 1.14.0line 1 is the problem as stated
2✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
undefined where 2*x - 1 = 0
3✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
undefined where 2*x - 1 = 0
undefined where Derivative(2*x - 1, x) = 0
4✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
undefined where Derivative(2*x - 1, x) = 0
5✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
6✓ 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 — 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 2026-10-05
  • qwen3.6:27b-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.