Limit of \( \displaystyle \frac{e^{6 x + 2} - 1}{\sin{\left(3 x + 1 \right)}} \) as \( x \to - \frac{1}{3} \)
Problem 1.176 · medium
Evaluate \( \displaystyle \lim_{x \to - \frac{1}{3}} \frac{e^{6 x + 2} - 1}{\sin{\left(3 x + 1 \right)}} \).
- \[ \lim_{x \to - \frac{1}{3}^+}\left(\frac{e^{6 x + 2} - 1}{\sin{\left(3 x + 1 \right)}}\right) \]limitIdentify the limit to evaluate.✓ Proved
- \[ = \lim_{x \to - \frac{1}{3}^+}\left(e^{6 x + 2} - 1\right) \left(\lim_{x \to - \frac{1}{3}^+} \sin{\left(3 x + 1 \right)}\right)^{-1} \]limit-lawCheck the limit of the numerator and denominator separately.Not checked
- \[ = \tilde{\infty} \lim_{x \to - \frac{1}{3}^+}\left(e^{6 x + 2} - 1\right) \]limitThe denominator approaches zero.Not checked
- \[ = \lim_{x \to - \frac{1}{3}^+} \text{NaN} \]limitThe numerator also approaches zero, creating an indeterminate form.Not checked
- \[ = \lim_{x \to - \frac{1}{3}^+}\left(\frac{\frac{d}{d x} \left(e^{6 x + 2} - 1\right)}{\frac{d}{d x} \sin{\left(3 x + 1 \right)}}\right) \]lhopitalApply L'Hopital's Rule because the limit is of the form 0/0.Not checked
- \[ = \lim_{x \to - \frac{1}{3}^+}\left(\frac{2 e^{6 x + 2}}{\cos{\left(3 x + 1 \right)}}\right) \]simplify algebraCompute the derivatives of the numerator and denominator. Simplify the constant coefficient.✓ Proved
- \[ = 2 \]substitution simplify simplify limitSubstitute the value x = -1/3 into the expression. Simplify the exponents and trigonometric arguments. Evaluate the exponential and trigonometric functions. Final result.✓ Proved
Answer \( 2 \)
Lines: 8 proved, 4 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.
The full receipt
| Line | Status | Checked by | Detail |
|---|---|---|---|
| 1 | ✓ Proved | sympy 1.14.0 | line 1 is the problem as stated |
| 2 | Not checked | — | simplify left nan; no point in the sample was defined on both lines undefined where sin(3*x + 1) = 0 undefined where Limit(sin(3*x + 1), x, -1/3, dir='+') = 0 |
| 3 | Not checked | — | simplify left nan; no point in the sample was defined on both lines undefined where Limit(sin(3*x + 1), x, -1/3, dir='+') = 0 |
| 4 | Not checked | — | simplify left nan; no point in the sample was defined on both lines |
| 5 | Not checked | — | simplify left nan; no point in the sample was defined on both lines undefined where Derivative(sin(3*x + 1), x) = 0 |
| 6 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 undefined where Derivative(sin(3*x + 1), x) = 0 undefined where cos(3*x + 1) = 0 |
| 7 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 undefined where cos(3*x + 1) = 0 |
| 8 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 undefined where cos(3*x + 1) = 0 |
| 9 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 |
| 10 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 |
| 11 | ✓ 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: fail (error) — Step 2 incorrectly applies the limit-law to split the quotient when the denominator’s limit is zero. The rule requires the denominator’s limit to be non‑zero; otherwise the split is invalid. This makes the subsequent steps based on that split incorrect.qwen3.6:27b-mlx: pass
Every verdict on record (4)
qwen3.6:27b-mlx: pass 2026-10-04gpt-oss:20b: fail (error) 2026-10-04 — Step 2 incorrectly applies the limit-law to split the quotient when the denominator’s limit is zero. The rule requires the denominator’s limit to be non‑zero; otherwise the split is invalid. This makes the subsequent steps based on that split incorrect.qwen3.6:27b-mlx: pass 2026-10-04 — The solution correctly applies L'Hopital's Rule to resolve the 0/0 indeterminate form. Each step changes only one aspect of the expression and uses valid labels from the fixed vocabulary.gpt-oss:20b: fail (style) 2026-10-04 — Step 11 uses the label "limit" but it is simply evaluating a numeric expression; the correct label would be "simplify".
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 2026-10-04 with SymPy 1.14.0.