Limit of \( \displaystyle \frac{- 3 x + e^{3 x} - 1}{9 x^{2}} \) as \( x \to 0 \)
Problem 1.74 · medium
Evaluate \( \displaystyle \lim_{x \to 0} \frac{- 3 x + e^{3 x} - 1}{9 x^{2}} \).
- \[ \lim_{x \to 0^+}\left(\frac{- 3 x + e^{3 x} - 1}{9 x^{2}}\right) \]limit algebraIdentify the limit to be evaluated. Rearrange the terms in the numerator.✓ Proved
- \[ = \lim_{x \to 0^+}\left(\frac{\frac{d}{d x} \left(- 3 x + e^{3 x} - 1\right)}{\frac{d}{d x} 9 x^{2}}\right) \]lhopitalApply L'Hépital's rule because the limit is an indeterminate form 0/0.✓ Proved
- \[ = \lim_{x \to 0^+}\left(\frac{3 e^{3 x} - 3}{18 x}\right) \]simplify factorCompute the derivatives. Factor out the constant 3 from the numerator.✓ Proved
- \[ = \lim_{x \to 0^+}\left(\frac{e^{3 x} - 1}{6 x}\right) \]simplifySimplify the fraction by dividing 3/18.✓ Proved
- \[ = \lim_{x \to 0^+}\left(\frac{\frac{d}{d x} \left(e^{3 x} - 1\right)}{\frac{d}{d x} 6 x}\right) \]lhopitalApply L'Hépital's rule again as it is still 0/0.✓ Proved
- \[ = \lim_{x \to 0^+}\left(\frac{e^{3 x}}{2}\right) \]simplify simplifyCompute the derivatives. Simplify the fraction 3/6 to 1/2.✓ Proved
- \[ = \frac{1}{2} \]limit simplifyEvaluate the limit by substituting x = 0. Final result.✓ Proved
Answer \( \frac{1}{2} \)
✓ 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 x = 0 |
| 3 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 undefined where x = 0 undefined where Derivative(9*x**2, x) = 0 |
| 4 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 undefined where Derivative(9*x**2, x) = 0 undefined where x = 0 |
| 5 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 undefined where x = 0 |
| 6 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 undefined where x = 0 |
| 7 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 undefined where x = 0 undefined where Derivative(6*x, x) = 0 |
| 8 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 undefined where Derivative(6*x, x) = 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: passqwen3.6:27b-mlx: pass
Every verdict on record (4)
qwen3.6:27b-mlx: pass 2026-10-03gpt-oss:20b: pass 2026-10-03qwen3.6:27b-mlx: pass 2026-09-30 — The solution correctly applies L'Hôpital's rule twice and handles algebraic simplifications in distinct steps. All labels are appropriate and the logic is sound.gpt-oss:20b: fail (style) 2026-09-30 — Step 4 is labeled "simplify" but it actually performs the differentiation step of L’Hôpital’s rule. The correct label should be "derivative" (or "lhopital" if the rule is still being applied).
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 2026-10-03 with SymPy 1.14.0.