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Ch. 4 - Applications of the Derivative
Briggs - Calculus: Early Transcendentals 3rd Edition
Briggs3rd EditionCalculus: Early TranscendentalsISBN: 9780136847243Non è quello che usi tu?Cambia libro di testo
Capitolo 4, Problema 4.7.25

Evaluate the following limits. Use l’Hôpital’s Rule when it is convenient and applicable.
lim_x→ e (ln x - 1) / (x - 1)

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First, identify the form of the limit as x approaches e. Substitute x = e into the expression (ln x - 1) / (x - 1). You will find that both the numerator and the denominator approach 0, which is an indeterminate form 0/0.
Since the limit is in the indeterminate form 0/0, l'Hôpital's Rule can be applied. According to l'Hôpital's Rule, if the limit of f(x)/g(x) as x approaches a is in the form 0/0 or ∞/∞, then the limit can be found by taking the derivative of the numerator and the derivative of the denominator.
Differentiate the numerator ln(x) - 1 with respect to x. The derivative of ln(x) is 1/x, and the derivative of the constant -1 is 0. Therefore, the derivative of the numerator is 1/x.
Differentiate the denominator x - 1 with respect to x. The derivative of x is 1, and the derivative of the constant -1 is 0. Therefore, the derivative of the denominator is 1.
Apply l'Hôpital's Rule by substituting the derivatives into the limit expression. The limit becomes lim_x→e (1/x) / 1. Simplify this expression to lim_x→e 1/x. Now, substitute x = e into the simplified expression to evaluate the limit.

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Limits

Limits are fundamental in calculus, representing the value that a function approaches as the input approaches a certain point. They are essential for understanding continuity, derivatives, and integrals. In this question, evaluating the limit as x approaches e involves determining the behavior of the function ln(x) - 1 over x - 1 near that point.
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One-Sided Limits

l'Hôpital's Rule

l'Hôpital's Rule is a method for evaluating limits that result in indeterminate forms, such as 0/0 or ∞/∞. It states that if the limit of f(x)/g(x) leads to an indeterminate form, the limit can be found by taking the derivative of the numerator and the derivative of the denominator. This rule is particularly useful in the given limit problem when direct substitution leads to an indeterminate form.
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Power Rules

Natural Logarithm

The natural logarithm, denoted as ln(x), is the logarithm to the base e, where e is approximately 2.71828. It is a crucial function in calculus, especially in limits and derivatives, due to its unique properties, such as ln(e) = 1 and its derivative being 1/x. In this limit problem, understanding the behavior of ln(x) as x approaches e is key to solving the limit.
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Derivative of the Natural Logarithmic Function
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