Limit of \( \displaystyle \frac{\tan{\left(2 x - 1 \right)}}{2 x - 1} \) as \( x \to \frac{1}{2} \)
Problem 1.356 · medium
Evaluate \( \displaystyle \lim_{x \to \frac{1}{2}} \frac{\tan{\left(2 x - 1 \right)}}{2 x - 1} \).
- \[ \lim_{x \to \frac{1}{2}^+}\left(\frac{\tan{\left(2 x - 1 \right)}}{2 x - 1}\right) \]limitStart with the original limit.✓ Proved
- \[ = \lim_{u \to 0^+}\left(\frac{\tan{\left(u \right)}}{u}\right) \]substitutionLet u = 2*x - 1. As x approaches 1/2, u approaches 0.✓ Proved
- \[ = \lim_{u \to 0^+}\left(\frac{\frac{d}{d u} \tan{\left(u \right)}}{\frac{d}{d u} u}\right) \]lhopitalApply L'Hopital's Rule since the limit is in the form 0/0.✓ Proved
- \[ = \lim_{u \to 0^+} \sec^{2}{\left(u \right)} \]simplifyCompute the derivatives of the numerator and denominator.✓ Proved
- \[ = 1 \]limit simplifyEvaluate the limit by plugging in u = 0. Simplify the final value.✓ 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 tan has poles at odd multiples of pi/2 undefined where 2*x - 1 = 0 undefined where u = 0 |
| 3 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 tan has poles at odd multiples of pi/2 undefined where u = 0 undefined where Derivative(u, u) = 0 |
| 4 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 tan has poles at odd multiples of pi/2 undefined where Derivative(u, u) = 0 sec has poles at odd multiples of pi/2 |
| 5 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 sec has poles at odd multiples of pi/2 |
| 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)
gpt-oss:20b: pass 2026-10-07qwen3.6:27b-mlx: pass 2026-10-07qwen3.6:27b-mlx: pass 2026-10-07 — The solution correctly applies substitution, L'Hopital's rule, and evaluation. Each step changes only one aspect of the expression and uses valid labels from the fixed vocabulary.gpt-oss:20b: pass 2026-10-07
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 2026-10-07 with SymPy 1.14.0.