Math Problem Statement

Find lim (x→∞) (e^x + x)^(1/x)

Solution

We need to evaluate the limit:

limx(ex+x)1/x.\lim_{x \to \infty} \left( e^x + x \right)^{1/x}.


Solution:

  1. Factor out exe^x from the term ex+xe^x + x:

ex+x=ex(1+xex).e^x + x = e^x \left( 1 + \frac{x}{e^x} \right).

This helps us split the expression into two parts.

  1. Rewrite the given limit:

(ex+x)1/x=[ex(1+xex)]1/x.\left( e^x + x \right)^{1/x} = \left[ e^x \left( 1 + \frac{x}{e^x} \right) \right]^{1/x}.

Using the property of exponents (ab)n=anbn(ab)^n = a^n \cdot b^n, we get:

(ex+x)1/x=(ex)1/x(1+xex)1/x.\left( e^x + x \right)^{1/x} = \left( e^x \right)^{1/x} \cdot \left( 1 + \frac{x}{e^x} \right)^{1/x}.

  1. Simplify each term:
  • First term: (ex)1/x\left( e^x \right)^{1/x}:

(ex)1/x=ex1x=e1=e.\left( e^x \right)^{1/x} = e^{x \cdot \frac{1}{x}} = e^1 = e.

  • Second term: (1+xex)1/x\left( 1 + \frac{x}{e^x} \right)^{1/x}:

As xx \to \infty, note that xex0\frac{x}{e^x} \to 0 because exe^x grows much faster than xx. Therefore:

1+xex1.1 + \frac{x}{e^x} \to 1.

Taking the 1/x1/x-th power:

(1+xex)1/x1.\left( 1 + \frac{x}{e^x} \right)^{1/x} \to 1.

  1. Combine the results:

Now combining both terms, we get:

(ex+x)1/x=e1=e.\left( e^x + x \right)^{1/x} = e \cdot 1 = e.


Final Answer:

limx(ex+x)1/x=e.\lim_{x \to \infty} \left( e^x + x \right)^{1/x} = e.


Would you like a deeper explanation of any step? Let me know!


Related Questions:

  1. What happens if xx \to \infty for a similar expression involving e2xe^{2x}?
  2. How does the rate of growth compare between exe^x and polynomial terms like xnx^n?
  3. How do we compute limits involving log(x)\log(x) or other logarithmic terms?
  4. What is the general method for solving exponential and logarithmic limits?
  5. How does the dominance of exe^x help simplify complicated limits?

Tip:

When working with exponential and polynomial terms, always factor out the dominant term to simplify the expression.

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Math Problem Analysis

Mathematical Concepts

Limits
Exponential Growth
Dominant Terms in Limits

Formulas

If f(x) grows much faster than g(x), then f(x) dominates: lim [f(x) + g(x)] ≈ f(x).
Exponentiation Rule: (a^b)^c = a^(b·c)

Theorems

Exponential functions grow faster than polynomial functions as x → ∞.
Laws of limits for exponential and dominant terms.

Suitable Grade Level

Undergraduate Calculus or Advanced High School