∫Calc Practice
Home›Calculus 1›L'Hôpital's rule›Problem 1.176

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 \( \displaystyle \lim_{x \to - \frac{1}{3}} \frac{e^{6 x + 2} - 1}{\sin{\left(3 x + 1 \right)}} \).
  1. \[ \lim_{x \to - \frac{1}{3}^+}\left(\frac{e^{6 x + 2} - 1}{\sin{\left(3 x + 1 \right)}}\right) \]
    limitIdentify the limit to evaluate.✓ Proved
  2. \[ = \lim_{x \to - \frac{1}{3}^+}\left(e^{6 x + 2} - 1\right) \left(\lim_{x \to - \frac{1}{3}^+} \sin{\left(3 x + 1 \right)}\right)^{-1} \]
    limit-lawCheck the limit of the numerator and denominator separately.Not checked
  3. \[ = \tilde{\infty} \lim_{x \to - \frac{1}{3}^+}\left(e^{6 x + 2} - 1\right) \]
    limitThe denominator approaches zero.Not checked
  4. \[ = \lim_{x \to - \frac{1}{3}^+} \text{NaN} \]
    limitThe numerator also approaches zero, creating an indeterminate form.Not checked
  5. \[ = \lim_{x \to - \frac{1}{3}^+}\left(\frac{\frac{d}{d x} \left(e^{6 x + 2} - 1\right)}{\frac{d}{d x} \sin{\left(3 x + 1 \right)}}\right) \]
    lhopitalApply L'Hopital's Rule because the limit is of the form 0/0.Not checked
  6. \[ = \lim_{x \to - \frac{1}{3}^+}\left(\frac{2 e^{6 x + 2}}{\cos{\left(3 x + 1 \right)}}\right) \]
    simplify algebraCompute the derivatives of the numerator and denominator. Simplify the constant coefficient.✓ Proved
  7. \[ = 2 \]
    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
LineStatusChecked byDetail
1✓ Provedsympy 1.14.0line 1 is the problem as stated
2Not 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
3Not 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
4Not checked—simplify left nan; no point in the sample was defined on both lines
5Not checked—simplify left nan; no point in the sample was defined on both lines
undefined where Derivative(sin(3*x + 1), x) = 0
6✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
undefined where Derivative(sin(3*x + 1), x) = 0
undefined where cos(3*x + 1) = 0
7✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
undefined where cos(3*x + 1) = 0
8✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
undefined where cos(3*x + 1) = 0
9✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
10✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
11✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
answer✓ Provedsympy 1.14.0final line against the stated answer: simplify(a - b) reduced to 0
answer, a second way✓ Provedsympy 1.14.0SymPy 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 2026-10-04
  • gpt-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.