∫Calc Practice

Limit of \( \displaystyle \frac{x - 5}{\sqrt{x - 1} - 2} \) as \( x \to 5 \)

Problem 1.220 · medium

Evaluate \( \displaystyle \lim_{x \to 5} \frac{x - 5}{\sqrt{x - 1} - 2} \).
  1. \[ \lim_{x \to 5^+}\left(\frac{x - 5}{\sqrt{x - 1} - 2}\right) \]
    limit algebraStart with the limit of the given function. Multiply the numerator and denominator by the conjugate of the denominator.✓ Proved
  2. \[ = \lim_{x \to 5^+}\left(\sqrt{x - 1} + 2\right) \]
    simplify simplify cancelSimplify the denominator using the difference of squares. Combine the constants in the denominator. Cancel the common factor (x - 5).✓ Proved
  3. \[ = 4 \]
    substitution simplify simplify limitSubstitute x = 5 into the expression. Simplify the expression inside the square root. Calculate the square root. Final result.✓ Proved
Answer \( 4 \)

✓ 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 sqrt(x - 1) - 2 = 0
3✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
undefined where sqrt(x - 1) - 2 = 0
4✓ Provedsympy 1.14.0simplify(a - b) reduced to 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
9✓ 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 2026-10-05
  • gpt-oss:20b: pass 2026-10-05
  • qwen3.6:27b-mlx: pass 2026-10-05 — The solution correctly applies algebraic manipulation (rationalization) to resolve the indeterminate form, followed by cancellation and substitution. Each step changes only one aspect of the expression and uses valid labels from the provided 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.