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Home›Calculus 1›L'Hôpital's rule›Problem 1.105

Limit of \( \displaystyle 2 x e^{- 2 x} \) as \( x \to \infty \)

Problem 1.105 · easy

Evaluate \( \displaystyle \lim_{x \to \infty} 2 x e^{- 2 x} \).
  1. \[ \lim_{x \to \infty}\left(2 x e^{- 2 x}\right) \]
    limit rewriteStart with the original limit expression. Rewrite the negative exponent as a fraction.✓ Proved
  2. \[ = \lim_{x \to \infty}\left(\frac{\frac{d}{d x} 2 x}{\frac{d}{d x} e^{2 x}}\right) \]
    lhopitalApply L'Hopital's Rule because the limit is of the form infinity/infinity.✓ Proved
  3. \[ = \lim_{x \to \infty} e^{- 2 x} \]
    simplify simplify rewriteCompute the derivatives of the numerator and denominator. Simplify the fraction by canceling the common factor of 2. Rewrite the expression with a negative exponent.✓ Proved
  4. \[ = 0 \]
    limitEvaluate the limit as x approaches infinity.✓ Proved
Answer \( 0 \)

✓ 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
LineStatusChecked byDetail
1✓ Provedsympy 1.14.0line 1 is the problem as stated
2✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
3✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
undefined where Derivative(exp(2*x), x) = 0
4✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
undefined where Derivative(exp(2*x), x) = 0
5✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
6✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
7✓ 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: pass
  • qwen3.6:27b-mlx: pass
Every verdict on record (4)
  • qwen3.6:27b-mlx: pass 2026-10-03
  • gpt-oss:20b: pass 2026-10-03
  • qwen3.6:27b-mlx: pass 2026-10-03 — The solution correctly applies L'Hopital's Rule and simplifies the resulting expression to evaluate the limit. Each step changes only one aspect of the expression and uses valid labels from the fixed vocabulary.
  • gpt-oss:20b: pass 2026-10-03

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.