Limit of \( \displaystyle \frac{\sin{\left(15 x - 5 \right)}}{\sin{\left(6 x - 2 \right)}} \) as \( x \to \frac{1}{3} \)
Problem 1.466 · medium
Evaluate \( \displaystyle \lim_{x \to \frac{1}{3}} \frac{\sin{\left(15 x - 5 \right)}}{\sin{\left(6 x - 2 \right)}} \).
- \[ \lim_{x \to \frac{1}{3}^+}\left(\frac{\sin{\left(15 x - 5 \right)}}{\sin{\left(6 x - 2 \right)}}\right) \]limitIdentify the limit and the indeterminate form.✓ Proved
- \[ = \lim_{x \to \frac{1}{3}^+}\left(\frac{\frac{d}{d x} \sin{\left(15 x - 5 \right)}}{\frac{d}{d x} \sin{\left(6 x - 2 \right)}}\right) \]lhopitalApply L'Hopital's Rule because the limit is of the form 0/0.✓ Proved
- \[ = \lim_{x \to \frac{1}{3}^+}\left(\frac{5 \cos{\left(15 x - 5 \right)}}{2 \cos{\left(6 x - 2 \right)}}\right) \]simplifyCompute the derivatives.✓ Proved
- \[ = \lim_{x \to \frac{1}{3}^+} \frac{5}{2} \]limitEvaluate the limit by substituting x = 1/3.✓ Proved
- \[ = \frac{5}{2} \]algebra simplify simplify simplify simplifySimplify the arguments of the trigonometric functions. Evaluate the arithmetic inside the cosine functions. Substitute the value of cos(0). Simplify the fraction. Final simplified value.✓ Proved
Answer \( \frac{5}{2} \)
✓ 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 sin(6*x - 2) = 0 undefined where Derivative(sin(6*x - 2), x) = 0 |
| 3 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 undefined where Derivative(sin(6*x - 2), x) = 0 undefined where cos(6*x - 2) = 0 |
| 4 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 undefined where cos(6*x - 2) = 0 |
| 5 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 |
| 6 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 |
| 7 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 |
| 8 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 |
| 9 | ✓ 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 2026-10-09qwen3.6:27b-mlx: pass 2026-10-09gpt-oss:20b: pass 2026-10-09qwen3.6:27b-mlx: pass 2026-10-09
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 2026-10-09 with SymPy 1.14.0.