Limits of sequences
Problem 7.376 · easy
Write the first four terms of \( \displaystyle a_n = \frac{\left(-1\right)^{n}}{n} \), and determine whether the sequence converges. If it does, find its limit.
- \[ \left[\begin{matrix}-1\\1 \cdot \frac{1}{2}\\- \frac{1}{3}\\1 \cdot \frac{1}{4}\end{matrix}\right] = \left[\begin{matrix}-1\\\frac{1}{2}\\- \frac{1}{3}\\\frac{1}{4}\end{matrix}\right] \]The first four terms.✓ Proved
- Squeeze: −1/n ≤ aₙ ≤ 1/n.Reviewed
- \[ \lim_{n \to \infty} \frac{1}{n} = 0 \]|aₙ| → 0, so aₙ → 0 by the squeeze theorem.✓ Proved
Answer \( a_1, \dots, a_4 = -1, \frac{1}{2}, - \frac{1}{3}, \frac{1}{4};\ 0 \)
✓ Nihil obstat Lines: 2 proved, 1 reviewed. 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 | simplify(lhs - rhs) reduced to 0 |
| 2 | Reviewed | reviewers: gpt-oss:20b, qwen3.6:27b-mlx | a sentence; read, not computed |
| 3 | ✓ 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 | the terms evaluated at n = 10⁶, 10⁶ + 1 and 10⁷ |
Reviewers
gpt-oss:20b: passqwen3.6:27b-mlx: pass — The solution correctly identifies the first four terms and applies the Squeeze Theorem with valid bounds to determine the limit.
Every verdict on record (4)
gpt-oss:20b: pass 2026-10-06qwen3.6:27b-mlx: pass 2026-10-06 — The solution correctly identifies the first four terms and applies the Squeeze Theorem with valid bounds to determine the limit.qwen3.6:27b-mlx: pass 2026-10-06 — The solution correctly identifies the first four terms and applies the Squeeze Theorem with valid bounds to determine the limit is 0.gpt-oss:20b: pass 2026-10-06
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/sequence_limits, checked 2026-10-06 with SymPy 1.14.0.