Math Problem Statement

Evaluate the limit: \( \lim_{x \to -\infty} \frac{2x}{e^x - x} \).

Solution

The expression in the image is:

limx2xexx\lim_{x \to -\infty} \frac{2x}{e^x - x}

To evaluate this limit, let's analyze the behavior of both the numerator and the denominator as xx approaches -\infty.

  1. Numerator: 2x2x as xx \to -\infty will tend towards -\infty.

  2. Denominator: exxe^x - x as xx \to -\infty:

    • The exponential function exe^x tends to 00 very rapidly because exponential decay is very fast as xx becomes large and negative.
    • The linear term x-x tends to ++\infty (since xx is negative, x-x is positive and large).

So, as xx approaches -\infty, the denominator exxe^x - x behaves approximately like x-x, because x-x dominates exe^x.

Thus, the limit simplifies to:

limx2xexxlimx2xx=limx2=2\lim_{x \to -\infty} \frac{2x}{e^x - x} \approx \lim_{x \to -\infty} \frac{2x}{-x} = \lim_{x \to -\infty} -2 = -2

So the limit is:

limx2xexx=2\lim_{x \to -\infty} \frac{2x}{e^x - x} = -2

Would you like more details on any part of this calculation?

Here are five related questions to expand on this concept:

  1. How would the limit change if the expression were limxx2exx\lim_{x \to -\infty} \frac{x^2}{e^x - x}?
  2. What happens to the limit if the numerator was exe^x instead of 2x2x?
  3. Can L'Hôpital's Rule be applied to solve this limit, and how would the process differ?
  4. How does the behavior of exponential functions compare with polynomial functions as xx tends to -\infty?
  5. How would you evaluate limx2xexx\lim_{x \to \infty} \frac{2x}{e^x - x}?

Tip: When dealing with limits involving exponential functions, always consider the dominant terms in the numerator and denominator, especially for large positive or negative values of xx.

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Math Problem Analysis

Mathematical Concepts

Limits
Exponential Functions
Asymptotic Behavior

Formulas

\( \lim_{x \to -\infty} \frac{2x}{e^x - x} \)

Theorems

Dominance of Exponential Decay
Behavior of Linear vs Exponential Functions

Suitable Grade Level

Grades 11-12