Math Problem Statement

Evaluate \(\lim_{x \to +\infty} \left(1 - \frac{2}{x}\right)^x\).

Solution

From the provided image, the expression under consideration is:

limx+(12x)x\lim_{x \to +\infty} \left(1 - \frac{2}{x}\right)^x

This is a limit problem involving an exponential expression. The steps to evaluate this limit are as follows:


Step 1: Recognize the Indeterminate Form

As x+x \to +\infty, the base 12x11 - \frac{2}{x} \to 1, and the exponent xx \to \infty. Hence, the expression is of the indeterminate form 11^\infty.


Step 2: Rewrite Using Logarithms

We rewrite the expression by setting it as eln[(12x)x]e^{\ln[(1 - \frac{2}{x})^x]}: limx+(12x)x=limx+exln(12x)\lim_{x \to +\infty} \left(1 - \frac{2}{x}\right)^x = \lim_{x \to +\infty} e^{x \ln\left(1 - \frac{2}{x}\right)}


Step 3: Simplify the Logarithmic Term

The natural logarithm ln(12x)\ln(1 - \frac{2}{x}) can be approximated for large xx using the expansion ln(1+u)u\ln(1 + u) \approx u when uu is small. Here, u=2xu = -\frac{2}{x}, so: ln(12x)2x.\ln\left(1 - \frac{2}{x}\right) \approx -\frac{2}{x}.

Substitute this back: xln(12x)x(2x)=2.x \ln\left(1 - \frac{2}{x}\right) \approx x \left(-\frac{2}{x}\right) = -2.


Step 4: Evaluate the Exponential Limit

Thus: limx+(12x)x=limx+e2=e2.\lim_{x \to +\infty} \left(1 - \frac{2}{x}\right)^x = \lim_{x \to +\infty} e^{-2} = e^{-2}.


Final Answer:

e2\boxed{e^{-2}}


Would you like further explanation, or should I clarify a specific step?
Here are five questions to deepen your understanding:

  1. Why does ln(12x)2x\ln(1 - \frac{2}{x}) \to -\frac{2}{x} for large xx?
  2. How does recognizing 11^\infty as an indeterminate form guide the solution process?
  3. What is the significance of using logarithmic transformations in exponential limits?
  4. How can the series expansion of ln(1+u)\ln(1 + u) be formally derived?
  5. What are other examples of limits involving indeterminate forms like 11^\infty?

Tip: For any indeterminate limit of the form 11^\infty, rewriting the base using the natural logarithm is a standard and reliable method.

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Math Problem Analysis

Mathematical Concepts

Limits
Exponential Growth
Natural Logarithms
Indeterminate Forms

Formulas

Natural logarithm approximation: \(\ln(1 + u) \approx u\) for small \(u\)
Exponential representation: \(e^{\ln(a^b)} = a^b\)

Theorems

Properties of logarithms
Exponential growth and limits involving \(e^x\)

Suitable Grade Level

Grades 11-12, College Level