Limit of \( \displaystyle \frac{\sin^{2}{\left(x + 1 \right)}}{\left(x + 1\right)^{2}} \) as \( x \to -1 \)
Problem 1.229 · medium
Evaluate \( \displaystyle \lim_{x \to -1} \frac{\sin^{2}{\left(x + 1 \right)}}{\left(x + 1\right)^{2}} \).
- \[ \lim_{x \to -1^+}\left(\frac{\sin^{2}{\left(x + 1 \right)}}{\left(x + 1\right)^{2}}\right) \]limit algebraIdentify the limit to evaluate. Rewrite the expression as a single squared term.✓ Proved
- \[ = \lim_{u \to 0^+}\left(\frac{\sin^{2}{\left(u \right)}}{u^{2}}\right) \]substitutionLet u = x + 1, so as x approaches -1, u approaches 0.✓ Proved
- \[ = \left(\lim_{u \to 0^+}\left(\frac{\sin{\left(u \right)}}{u}\right)\right)^{2} \]limit-lawApply the power rule for limits.✓ Proved
- \[ = \lim_{u \to 0^+} 1 \]trig-limitUse the fundamental trigonometric limit sin(u)/u -> 1.✓ Proved
- \[ = 1 \]simplifyThe limit evaluates to 1.✓ Proved
Answer \( 1 \)
✓ 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
| Line | Status | Checked by | Detail |
|---|---|---|---|
| 1 | ✓ Proved | sympy 1.14.0 | line 1 is the problem as stated |
| 2 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 undefined where x + 1 = 0 |
| 3 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 undefined where x + 1 = 0 undefined where u = 0 |
| 4 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 undefined where u = 0 |
| 5 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 undefined where u = 0 |
| 6 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 |
| answer | ✓ Proved | sympy 1.14.0 | final line against the stated answer: simplify(a - b) reduced to 0 |
| answer, a second way | ✓ Proved | sympy 1.14.0 | SymPy took the limit from both sides and got the stated value |
Reviewers
gpt-oss:20b: passqwen3.6:27b-mlx: pass
Every verdict on record (4)
qwen3.6:27b-mlx: pass 2026-10-05gpt-oss:20b: pass 2026-10-05qwen3.6:27b-mlx: pass 2026-10-05 — The solution correctly applies substitution, limit laws, and the standard trigonometric limit. Each step changes only one aspect of the expression 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.