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Evaluate a limit at infinity using L'Hopital's Rule

Consider the function h(x)=ln⁡(x)x.h(x) = \frac{\ln(x)}{x}. Evaluate lim⁡x→∞ln⁡(x)x.\lim_{x \to \infty} \frac{\ln(x)}{x}. Verify that the limit is in an indeterminate form before applying L'Hopital's Rule, then compute the limit.

Hint

Check that direct substitution gives the form ∞/∞\infty/\infty. Then differentiate the numerator and denominator separately (do not use the quotient rule), and simplify the resulting expression before taking the limit again.

Step-by-step solution

As x→∞x \to \infty, ln⁡(x)→∞\ln(x) \to \infty and x→∞x \to \infty, so the limit has the indeterminate form ∞/∞\infty/\infty. This justifies applying L'Hopital's Rule, which requires differentiating the numerator and denominator separately: ddx[ln⁡(x)]=1x\frac{d}{dx}[\ln(x)] = \frac{1}{x} and ddx[x]=1\frac{d}{dx}[x] = 1.

Applying the rule gives lim⁡x→∞ln⁡(x)x=lim⁡x→∞1/x1=lim⁡x→∞1x.\lim_{x \to \infty} \frac{\ln(x)}{x} = \lim_{x \to \infty} \frac{1/x}{1} = \lim_{x \to \infty} \frac{1}{x}. As x→∞x \to \infty, 1/x→01/x \to 0, so the original limit equals 00.

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