Math Problem Statement

f(x) = (x^2 - 4) / (sqrt(x) - sqrt(2)), then lim_{x → 2} f(x) is equivalent to which of the following?

Solution

The given function is:

f(x)=x24x2f(x) = \frac{x^2 - 4}{\sqrt{x} - \sqrt{2}}

We are asked to find the limit as x2x \to 2:

limx2f(x)\lim_{x \to 2} f(x)

Let's solve this step by step. The function appears to have the indeterminate form 00\frac{0}{0} at x=2x = 2, so we can apply algebraic manipulation to resolve this indeterminate form.

The expression x24x^2 - 4 can be factored as:

x24=(x2)(x+2)x^2 - 4 = (x - 2)(x + 2)

Thus, the function becomes:

f(x)=(x2)(x+2)x2f(x) = \frac{(x - 2)(x + 2)}{\sqrt{x} - \sqrt{2}}

We now need to simplify this further to resolve the limit at x=2x = 2. To do this, we'll rationalize the denominator x2\sqrt{x} - \sqrt{2} by multiplying both the numerator and denominator by x+2\sqrt{x} + \sqrt{2}:

(x2)(x+2)x2×x+2x+2=(x2)(x+2)(x+2)x2\frac{(x - 2)(x + 2)}{\sqrt{x} - \sqrt{2}} \times \frac{\sqrt{x} + \sqrt{2}}{\sqrt{x} + \sqrt{2}} = \frac{(x - 2)(x + 2)(\sqrt{x} + \sqrt{2})}{x - 2}

The x2x - 2 terms cancel out, leaving:

f(x)=(x+2)(x+2)f(x) = (x + 2)(\sqrt{x} + \sqrt{2})

Now, we can substitute x=2x = 2 directly into the simplified expression:

f(2)=(2+2)(2+2)=4(22)=82f(2) = (2 + 2)(\sqrt{2} + \sqrt{2}) = 4(2\sqrt{2}) = 8\sqrt{2}

Thus, the limit is:

limx2f(x)=82\lim_{x \to 2} f(x) = 8\sqrt{2}

If you have any questions or need further clarification, let me know!

Here are 5 related questions for further practice:

  1. How would you evaluate limx2x29x3\lim_{x \to 2} \frac{x^2 - 9}{\sqrt{x} - 3}?
  2. How do you rationalize the denominator in 152\frac{1}{\sqrt{5} - 2}?
  3. What are the indeterminate forms in limits, and how do you recognize them?
  4. How can L'Hopital's Rule be applied to resolve indeterminate limits?
  5. What is the general approach to factoring differences of squares?

Tip: When limits yield indeterminate forms like 00\frac{0}{0}, always check for algebraic simplifications such as factoring or rationalizing.

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Math Problem Analysis

Mathematical Concepts

Limits
Rationalization
Indeterminate Forms
Factoring

Formulas

Difference of squares: x^2 - a^2 = (x - a)(x + a)
Rationalization: Multiply numerator and denominator by the conjugate

Theorems

Limit Theorem for Indeterminate Forms
Difference of Squares

Suitable Grade Level

Grades 11-12 or early university calculus