Estimating a limit from a table
Problem 1.597 · easy
Make a table of values of \( \displaystyle f(x) = \frac{x^{2} - 3 x}{x^{2} + 3 x} \) at \( \displaystyle x = 0 \pm 0.1,\ 0 \pm 0.01,\ 0 \pm 0.001,\ 0 \pm 0.0001 \) and use it to estimate \( \displaystyle \lim_{x \to 0} f(x) \).
- f(0) itself is undefined (0/0), so the table approaches 0 from both sides.
- The table: f(0 − 0.1) ≈ -1.06896552; f(0 − 0.01) ≈ -1.00668896; f(0 − 0.001) ≈ -1.00066689; f(0 − 0.0001) ≈ -1.00006667; f(0 + 0.0001) ≈ -9.99933336e-1; f(0 + 0.001) ≈ -9.99333555e-1; f(0 + 0.01) ≈ -9.93355482e-1; f(0 + 0.1) ≈ -9.35483871e-1.
- From both sides the values settle toward -1.000000.
- \[ \lim_{x \to 0}\left(\frac{x^{2} - 3 x}{x^{2} + 3 x}\right) = -1 \]The exact (two-sided) limit agrees with the table.✓ Proved
Answer \( \lim_{x\to 0} f(x) = -1 \approx -1.000000 \)
Lines: 1 proved, 3 not checked. The answer was also checked a second way, without looking at the solution. The reviewers disagree about how one step is explained; every verdict is in the receipt. How we verify
The full receipt
| Line | Status | Checked by | Detail |
|---|---|---|---|
| 1 | Not checked | — | a sentence; read, not computed |
| 2 | Not checked | — | a sentence; read, not computed |
| 3 | Not checked | — | a sentence; read, not computed |
| 4 | ✓ Proved | sympy 1.14.0 | simplify(lhs - rhs) reduced to 0 |
| answer, a second way | ✓ Checked independently | sympy 1.14.0 + mpmath 1.3.0 | f evaluated at a ± 10⁻⁹ in 30-digit arithmetic |
Reviewers
gpt-oss:20b: fail (misleading) — Sentence 1 incorrectly states that the table approaches 0 from both sides; the function actually approaches -1, not 0. This misleads a student about the behavior near the discontinuity.qwen3.6:27b-mlx: pass — The solution correctly identifies the indeterminate form, provides accurate numerical approximations for the specified points, and correctly concludes the limit is -1.
Every verdict on record (6)
qwen3.6:27b-mlx: pass 2026-10-17 — The solution correctly identifies the indeterminate form, provides accurate numerical approximations for the specified points, and correctly concludes the limit is -1.gpt-oss:20b: fail (misleading) 2026-10-17 — Sentence 1 incorrectly states that the table approaches 0 from both sides; the function actually approaches -1, not 0. This misleads a student about the behavior near the discontinuity.qwen3.6:27b-mlx: pass 2026-10-14 — The solution correctly identifies the indeterminate form, provides accurate numerical approximations for the specified points, and correctly concludes the limit is -1.gpt-oss:20b: fail (misleading) 2026-10-14 — Sentence 1 incorrectly states that the table approaches 0 from both sides; it should say the values approach -1. The rest of the solution is correct.qwen3.6:27b-mlx: pass 2026-10-14 — The solution correctly identifies the undefined nature of f(0), provides accurate numerical evaluations for the specified points, and correctly infers the limit from the table. The final symbolic check confirms the result.gpt-oss:20b: fail (error) 2026-10-14 — Sentence 1 incorrectly states that the table approaches 0 from both sides; the function actually approaches –1 as x→0. The rest of the solution is fine, but the misleading statement invalidates the setup.
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
generator:structured/limit_table, checked 2026-10-17 with SymPy 1.14.0.