Math Problem Statement

Ein rasjonal funksjon har ein vertikal asymptote for x = 2, og ein horisontal asymptote for y = -4. Finn eit mogeleg funksjonsuttrykk for denne funksjonen. Vis utrekning eller forklar korleis du tenkjer.

Solution

To solve this problem, we need to construct a rational function f(x)f(x) with the following properties:

  1. A vertical asymptote at x=2x = 2. This means the denominator of the function should be zero when x=2x = 2.
  2. A horizontal asymptote at y=4y = -4. This means as xx \to \infty, the function f(x)f(x) should approach 4-4.

Step-by-Step Solution:

1. Vertical Asymptote

A vertical asymptote at x=2x = 2 implies that the denominator has a factor of (x2)(x - 2). Thus, the function will be of the form:

f(x)=N(x)D(x)=N(x)x2f(x) = \frac{N(x)}{D(x)} = \frac{N(x)}{x - 2}

where N(x)N(x) is the numerator.

2. Horizontal Asymptote

For a horizontal asymptote at y=4y = -4, the degrees of the numerator N(x)N(x) and denominator D(x)D(x) must be the same. Moreover, the leading coefficient of the numerator divided by the leading coefficient of the denominator should equal 4-4. If the denominator is x2x - 2, the numerator N(x)N(x) must be 4x+c-4x + c, where cc is a constant.

Thus, a possible function is:

f(x)=4x+cx2.f(x) = \frac{-4x + c}{x - 2}.

3. Simplifying

We don't need cc to create a horizontal asymptote; it only shifts the function vertically. The simplest possible function satisfying both conditions is:

f(x)=4xx2.f(x) = \frac{-4x}{x - 2}.

Let’s rewrite it to include the horizontal asymptote explicitly:

f(x)=4xx2.f(x) = \frac{-4x}{x - 2}.

Verification:

  1. Vertical Asymptote at x=2x = 2: When x=2x = 2, the denominator becomes zero, creating a vertical asymptote.

  2. Horizontal Asymptote at y=4y = -4: As xx \to \infty, the terms of highest degree dominate. For large xx, f(x)4f(x) \approx -4, matching the desired horizontal asymptote.


Would you like a more detailed breakdown of the reasoning or have any specific questions about this function?

Follow-up Questions:

  1. What happens to the function behavior as xx \to -\infty?
  2. How does adding constants to the numerator affect the horizontal asymptote?
  3. Can there be more than one rational function satisfying these conditions?
  4. What is the domain of the constructed function?
  5. How do vertical and horizontal asymptotes affect the graph?

Tip:

When constructing rational functions, always check the degrees of the numerator and denominator for horizontal asymptotes and the factors of the denominator for vertical asymptotes.

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Math Problem Analysis

Mathematical Concepts

Rational Functions
Asymptotes
Function Analysis

Formulas

Horizontal Asymptote: Leading coefficients of numerator and denominator
Vertical Asymptote: Denominator equals zero

Theorems

Degree comparison for horizontal asymptotes

Suitable Grade Level

Grades 10-12