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In Problems \(25-30\), describe the form of the limit \((0 / 0\) \(\infty / \infty, \infty \cdot 0, \infty-\infty, 1^{\infty}, 0^{0}, \infty^{0},\) or none of these). Does I'Hopital's rule apply? If so, explain how. $$\lim _{x \rightarrow 0}(1+x)^{x}$$

Short Answer

Expert verified
The limit is 1; L'Hopital's Rule is not directly applicable.

Step by step solution

01

Identify the Limit Form

We need to evaluate \( \lim _{x \rightarrow 0}(1+x)^{x} \). First, substitute \( x = 0 \) directly into the expression to understand the indeterminate form. This gives \( (1+0)^{0} = 1^{0} \), which is indeed an indeterminate form.
02

Determine if L'Hopital's Rule Applies

L'Hopital's Rule applies to indeterminate forms of the type \( \frac{0}{0} \) or \( \frac{\infty}{\infty} \). Given our form of \( 1^{0} \), L'Hopital's Rule does not directly apply, hence we need to use a different approach.
03

Rewriting the Expression

To handle the \( 1^{0} \) indeterminate form, let's take the natural logarithm of the expression: \( \ln((1+x)^x) = x \cdot \ln(1+x) \). Now, consider the limit: \( \lim_{x \to 0} x \ln(1+x) \).
04

Apply L'Hopital's Rule

Rewrite \( x \ln(1+x) \) as \( \frac{\ln(1+x)}{1/x} \). Both the numerator and the denominator approach 0 as \( x \to 0 \), resulting in the \( \frac{0}{0} \) form. L'Hopital's Rule can now be applied here. Differentiate the numerator and denominator: \( \frac{d}{dx} \ln(1+x) = \frac{1}{1+x} \), \( \frac{d}{dx}(1/x) = -1/x^2 \).
05

Evaluate the New Limit

The limit now becomes \( \lim_{x \to 0} \frac{\frac{1}{1+x}}{-1/x^2} = \lim_{x \to 0} \frac{-x^2}{1+x} \). Simplifying this gives \( \lim_{x \to 0} -x^2 = 0 \). Therefore, \( \ln(L) = 0 \), where \( L \) is the original limit. Hence, \( L = e^0 = 1 \).
06

Conclusion

Since the natural logarithm of the limit confirms it approaches 1, the original limit \( \lim_{x \to 0}(1+x)^{x} = 1 \).

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Key Concepts

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

Indeterminate Forms
When tackling limits in calculus, you might come across expressions that are not straightforward to evaluate. These expressions are known as indeterminate forms. It's like a question mark in mathematics, where direct substitution does not reveal the limit clearly. Indeterminate forms include types like:
  • \(0/0\)
  • \(\infty/\infty\)
  • \(\infty \cdot 0\)
  • \(\infty - \infty\)
  • \(1^{\infty}\)
  • \(0^0\)
  • \(\infty^0\)
In our exercise, we encounter the form \(1^0\) when substituting \(x = 0\) directly into \((1+x)^x\). This is a classic indeterminate form, and while L'Hôpital's Rule helps with \(0/0\) or \(\infty/\infty\), it doesn't directly apply here. Instead, mathematicians employ other strategies to resolve these cases.
Limit Evaluation
Evaluating limits of indeterminate forms requires creative tactics to simplify the expression into a determinate form. One such method involves rewriting the expression, as seen in the step-by-step solution for \( \lim_{x \rightarrow 0}(1+x)^{x}\).
When we face indeterminate forms like \(1^0\), taking the natural logarithm of the expression is very useful. This introduces a more manageable form for limit evaluation, by typically transforming the problem into a multiplicative format that's easier to differentiate or apply other calculus strategies.
In our case, we transformed \((1+x)^x\) to \(x \ln(1+x)\), which could be rewritten as \(\frac{\ln(1+x)}{1/x}\). Now, both parts of this fraction are in a \(0/0\) form as \(x \to 0\). This is where we can cleverly deploy L'Hôpital's Rule to differentiate and find the limit effectively.
Natural Logarithm
The natural logarithm, denoted as \(\ln(x)\), is a fundamental function in mathematics. It is the inverse of the exponential function with base \(e\), making it particularly powerful in calculus for dealing with exponential expressions.
In our exercise, taking the natural logarithm of \((1+x)^x\) simplifies the expression into \(x \ln(1+x)\). This transformation makes subsequent steps easier, allowing us to convert a power into a product, and then into a fraction more amenable to L'Hôpital's Rule.
Here's how the algebra works in favor of simplification:
  • The product \(x \ln(1+x)\) unfolds complex exponential behaviors into simple multiplicative changes.
  • Applying \(\ln\) helps reduce the complexity, liberating the problem from difficult power terms.
  • Once simplified, taking derivatives becomes straightforward, enabling the evaluation of the limit.
The natural logarithm acts as a bridge, connecting the complex world of exponentials with the intuitive strategies of calculus.

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