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Find the limit. Use I'Hopital's rule if it applies. $$\lim _{x \rightarrow 1} \frac{\ln x}{x-1}$$

Short Answer

Expert verified
The limit is 1.

Step by step solution

01

Identify the Indeterminate Form

First, substitute \( x = 1 \) into the expression \( \frac{\ln x}{x-1} \) to check if it forms an indeterminate type. Substituting gives \( \frac{\ln 1}{1-1} = \frac{0}{0} \), which is an indeterminate form. This means we can apply L'Hôpital's Rule.
02

Apply L'Hôpital's Rule

L'Hôpital's Rule states that if a limit of the form \( \frac{0}{0} \) or \( \frac{\infty}{\infty} \) is encountered, the limit \( \lim_{x \to c} \frac{f(x)}{g(x)} \) can be found by calculating \( \lim_{x \to c} \frac{f'(x)}{g'(x)} \) provided this limit exists. Differentiate the numerator and the denominator separately.
03

Differentiate Numerator and Denominator

The derivative of \( \ln x \) with respect to \( x \) is \( \frac{1}{x} \). The derivative of \( x - 1 \) with respect to \( x \) is \( 1 \). Thus, applying L'Hôpital's Rule gives us the new limit \( \lim_{x \to 1} \frac{\frac{1}{x}}{1} = \lim_{x \to 1} \frac{1}{x} \).
04

Evaluate the New Limit

Now, substitute \( x = 1 \) into the expression \( \frac{1}{x} \). This results in \( \frac{1}{1} = 1 \). Therefore, the original limit evaluates to \( 1 \).

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Indeterminate Forms
Indeterminate forms are expressions that arise in calculus when evaluating limits, and they require special methods to resolve. A common indeterminate form is \( \frac{0}{0} \), which suggests that both the numerator and denominator approach zero.When such forms occur, typical arithmetic rules aren't sufficient, and techniques like L'Hôpital's Rule become essential. This rule helps us bypass the direct calculation and use derivatives to find the limit instead.Knowing how to identify an indeterminate form is the first step when resolving a limit problem. Without recognition, one might use incorrect methods leading to wrong conclusions.
Limit Evaluation
Limit evaluation is a fundamental concept in calculus that involves finding the value that a function approaches as the input approaches a certain point. In the exercise, we are finding the limit as \( x \) approaches 1 for the function \( \frac{\ln x}{x-1} \).Evaluating limits can sometimes result in determinate forms like a specific number. However, when an indeterminate form arises, special approaches, such as L'Hôpital's Rule, are applied to accurately determine the limit.Limits are essential for understanding the behavior of functions at points that are not explicitly defined within the function itself.
Differentiation
Differentiation refers to finding the derivative of a function, which provides the rate of change of the function's output with respect to its input. It is crucial in applying L'Hôpital's Rule.- The derivative of a function gives us another function that describes this rate of change.- In our example, differentiation is applied to both \( \ln x \) and \( x-1 \).For the natural logarithm \( \ln x \), the derivative is \( \frac{1}{x} \). And for \( x-1 \), the derivative is simply 1. These derivatives are then used to transform the original limit problem into a simpler one, \( \lim_{x \to 1} \frac{1}{x} \). This is feasible and gives us a clean evaluation of the original limit problem.
Natural Logarithm
The natural logarithm \( \ln x \) is a logarithm to the base \( e \), where \( e \) is an important mathematical constant approximately equal to 2.71828. The natural logarithm is widely used in calculus due to its simple derivative.- The derivative of \( \ln x \) is \( \frac{1}{x} \), which makes it easy to work with when applying calculus techniques like L'Hôpital's Rule.- This simplicity is due to the property that \( e^x \) is its own derivative, a unique feature of exponential and logarithmic functions.In the exercise, knowing that the natural logarithm allows straightforward differentiation supported the application of L'Hôpital’s Rule, making it possible to evaluate the otherwise indeterminate form to find the limit effectively.

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