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Ch. 7 - Transcendental Functions
Hass - Thomas' Calculus 15th Edition
Hass15th EditionThomas' CalculusISBN: 9780137616077Non è quello che usi tu?Cambia libro di testo
Capitolo 7, Problema 7.5.66

Indeterminate Powers and Products
Find the limits in Exercises 53–68.
66. lim (x → 0⁺) x (ln x)²

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1
Identify the form of the limit as \(x \to 0^+\) for the expression \(x (\ln x)^2\). Notice that as \(x\) approaches \(0\) from the right, \(x\) approaches \(0\) and \(\ln x\) approaches \(-\infty\), so \((\ln x)^2\) approaches \(+\infty\). This creates an indeterminate form of type \(0 \cdot \infty\).
Rewrite the expression to transform the product into a quotient, which is often easier to analyze with L'Hôpital's Rule. For example, write \(x (\ln x)^2\) as \(\frac{(\ln x)^2}{\frac{1}{x}}\).
Check the new limit form as \(x \to 0^+\). Since \(\ln x \to -\infty\), \((\ln x)^2 \to +\infty\), and \(\frac{1}{x} \to +\infty\), the limit becomes an indeterminate form \(\frac{\infty}{\infty}\), suitable for applying L'Hôpital's Rule.
Apply L'Hôpital's Rule by differentiating the numerator and denominator separately with respect to \(x\). The derivative of the numerator \((\ln x)^2\) is \(2 \ln x \cdot \frac{1}{x}\), and the derivative of the denominator \(\frac{1}{x}\) is \(-\frac{1}{x^2}\).
Simplify the resulting expression after differentiation and analyze the new limit as \(x \to 0^+\). This process will help determine the behavior of the original limit.

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