∫Calc Practice

Limit of \( \displaystyle \frac{4 \left(2 x - 1\right)^{2} - 1}{2 x + 2 \left(2 x - 1\right)^{2} - 1} \) as \( x \to \infty \)

Problem 1.65 · hard

Evaluate \( \displaystyle \lim_{x \to \infty} \frac{4 \left(2 x - 1\right)^{2} - 1}{2 x + 2 \left(2 x - 1\right)^{2} - 1} \).
  1. \[ \lim_{x \to \infty}\left(\frac{4 \left(2 x - 1\right)^{2} - 1}{2 x + 2 \left(2 x - 1\right)^{2} - 1}\right) \]
    limitStarting with the original limit expression.✓ Proved
  2. \[ = \lim_{x \to \infty}\left(\frac{16 x^{2} - 16 x + 3}{8 x^{2} - 6 x + 1}\right) \]
    algebra algebra simplifyExpand the squared term (2x - 1)^2. Distribute the constants into the parentheses. Combine like terms in the numerator and denominator.✓ Proved
  3. \[ = \lim_{x \to \infty}\left(\frac{16 x^{2}}{8 x^{2} - 6 x + 1} - \frac{16 x}{8 x^{2} - 6 x + 1} + \frac{3}{8 x^{2} - 6 x + 1}\right) \]
    limit-lawSplit the limit into three separate parts using limit laws.✓ Proved
  4. \[ = - \lim_{x \to \infty}\left(\frac{16 x}{8 x^{2} - 6 x + 1}\right) + \lim_{x \to \infty}\left(\frac{16 x^{2}}{8 x^{2} - 6 x + 1}\right) + \lim_{x \to \infty}\left(\frac{3}{8 x^{2} - 6 x + 1}\right) \]
    limit-lawApply the limit to each term individually.✓ Proved
  5. \[ = \lim_{x \to \infty} 2 - \lim_{x \to \infty}\left(\frac{16 x}{8 x^{2} - 6 x + 1}\right) + \lim_{x \to \infty}\left(\frac{3}{8 x^{2} - 6 x + 1}\right) \]
    simplifyDivide the first term's numerator and denominator by x^2.✓ Proved
  6. \[ = 2 - \lim_{x \to \infty}\left(\frac{16 x}{8 x^{2} - 6 x + 1}\right) + \lim_{x \to \infty}\left(\frac{3}{8 x^{2} - 6 x + 1}\right) \]
    simplifyEvaluate the limit of the first term.✓ Proved
  7. \[ = 2 - \lim_{x \to \infty}\left(\frac{16}{8 x - 6 + \frac{1}{x}}\right) + \lim_{x \to \infty}\left(\frac{3}{8 x^{2} - 6 x + 1}\right) \]
    algebraDivide the second term's numerator and denominator by x.✓ Proved
  8. \[ = 2 + \lim_{x \to \infty}\left(\frac{3}{8 x^{2} - 6 x + 1}\right) \]
    limitEvaluate the limit of the second term as x approaches infinity.✓ Proved
  9. \[ = 2 \]
    limit simplifyEvaluate the limit of the third term as x approaches infinity. Final calculation.✓ Proved
Answer \( 2 \)

✓ 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 + 2*(2*x - 1)**2 - 1 = 0
undefined where 8*x**2 - 6*x + 1 = 0
3✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
undefined where 8*x**2 - 6*x + 1 = 0
4✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
undefined where 8*x**2 - 6*x + 1 = 0
5✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
undefined where 8*x**2 - 6*x + 1 = 0
6✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
undefined where 8*x**2 - 6*x + 1 = 0
7✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
undefined where 8*x**2 - 6*x + 1 = 0
8✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
undefined where 8*x**2 - 6*x + 1 = 0
9✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
undefined where 8*x**2 - 6*x + 1 = 0
undefined where 8*x - 6 + 1/x = 0
undefined where x = 0
10✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
undefined where 8*x - 6 + 1/x = 0
undefined where 8*x**2 - 6*x + 1 = 0
undefined where x = 0
11✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
undefined where 8*x**2 - 6*x + 1 = 0
12✓ 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 limit laws and algebraic simplifications to evaluate the limit at infinity. Each step adheres to the single-rule constraint and uses valid labels from the fixed vocabulary.
Every verdict on record (4)
  • qwen3.6:27b-mlx: pass 2026-10-03 — The solution correctly applies limit laws and algebraic simplifications to evaluate the limit at infinity. Each step adheres to the single-rule constraint and uses valid labels from the fixed vocabulary.
  • gpt-oss:20b: pass 2026-10-03
  • qwen3.6:27b-mlx: pass 2026-09-30 — The solution correctly expands, simplifies, and splits the limit into manageable terms. Each step applies a single rule appropriately, and the logic for evaluating the limits of the individual terms is sound.
  • gpt-oss:20b: pass 2026-09-30

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 2026-10-03 with SymPy 1.14.0.