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Limit of e^x/x^2 as x approaches infinity using L'Hopital's Rule

Evaluate the following limit, which involves an indeterminate form.

Consider the function f(x)=exx2.f(x) = \frac{e^x}{x^2}. Evaluate lim⁡x→∞exx2.\lim_{x \to \infty} \frac{e^x}{x^2}.

Hint

First check that direct substitution gives an indeterminate form of type ∞/∞\infty/\infty. Since both numerator and denominator are differentiable and grow without bound, apply L'Hopital's Rule by differentiating numerator and denominator separately. You may need to apply the rule more than once — check the indeterminate form each time before doing so.

Step-by-step solution

As x→∞x \to \infty, both ex→∞e^x \to \infty and x2→∞x^2 \to \infty, so the limit has the indeterminate form ∞/∞\infty/\infty. This justifies applying L'Hopital's Rule: differentiate the numerator and denominator separately (not using the quotient rule) to get lim⁡x→∞exx2=lim⁡x→∞ex2x.\lim_{x\to\infty} \frac{e^x}{x^2} = \lim_{x\to\infty} \frac{e^x}{2x}.

The new limit lim⁡x→∞ex2x\lim_{x\to\infty} \frac{e^x}{2x} is again of the form ∞/∞\infty/\infty, so L'Hopital's Rule applies once more: differentiating top and bottom gives lim⁡x→∞ex2x=lim⁡x→∞ex2.\lim_{x\to\infty} \frac{e^x}{2x} = \lim_{x\to\infty} \frac{e^x}{2}. As x→∞x \to \infty, ex→∞e^x \to \infty, so this limit is ∞\infty, meaning the original limit diverges to infinity.

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