Math Problem Statement

Find lim f(x) as x approaches infinity given the inequality: (10e^x - 23) / (2e^x) < f(x) < (5√x) / (√x - 1) for x > 1.

Solution

We are tasked with finding limxf(x)\lim_{{x \to \infty}} f(x), given that for all x>1x > 1, the function f(x)f(x) satisfies the inequality:

10ex232ex<f(x)<5xx1.\frac{10e^x - 23}{2e^x} < f(x) < \frac{5\sqrt{x}}{\sqrt{x-1}}.

Step 1: Investigate the left-hand side limit as xx \to \infty

The left-hand side expression is:

10ex232ex=10ex2ex232ex=5232ex.\frac{10e^x - 23}{2e^x} = \frac{10e^x}{2e^x} - \frac{23}{2e^x} = 5 - \frac{23}{2e^x}.

As xx \to \infty, the term 232ex0\frac{23}{2e^x} \to 0 because exe^x grows exponentially. Therefore:

limx(5232ex)=5.\lim_{{x \to \infty}} \left( 5 - \frac{23}{2e^x} \right) = 5.

Step 2: Investigate the right-hand side limit as xx \to \infty

Now let's examine the right-hand side expression:

5xx1.\frac{5\sqrt{x}}{\sqrt{x-1}}.

For large xx, we can approximate x1x\sqrt{x - 1} \approx \sqrt{x}. Hence:

5xx15xx=5.\frac{5\sqrt{x}}{\sqrt{x-1}} \approx \frac{5\sqrt{x}}{\sqrt{x}} = 5.

Thus, as xx \to \infty:

limx5xx1=5.\lim_{{x \to \infty}} \frac{5\sqrt{x}}{\sqrt{x-1}} = 5.

Step 3: Apply the Squeeze Theorem

We now have the following situation as xx \to \infty:

5f(x)5.5 \leq f(x) \leq 5.

By the Squeeze Theorem, since both bounds approach 5, we conclude that:

limxf(x)=5.\lim_{{x \to \infty}} f(x) = 5.

Thus, the limit of f(x)f(x) as xx \to \infty is 5.

Would you like more details on any step, or do you have any further questions?


Here are five related questions to explore:

  1. What is the Squeeze Theorem, and how does it apply in this case?
  2. How do exponential functions behave as xx \to \infty?
  3. How do you approximate square roots of large numbers, like x1\sqrt{x - 1}?
  4. Can you apply the Squeeze Theorem to other types of inequalities?
  5. What would happen if the limits of the upper and lower bounds were not equal?

Tip: Always check the behavior of functions like exponentials and roots as xx \to \infty, as they often simplify in the limit.

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Math Problem Analysis

Mathematical Concepts

Limits
Inequalities
Exponential Functions
Square Roots

Formulas

lim x→∞ (10e^x - 23) / (2e^x)
lim x→∞ (5√x) / (√x - 1)

Theorems

Squeeze Theorem

Suitable Grade Level

College Level - Calculus