Math Problem Statement

find an equation for f

Consider a rational function f that satisfies the following conditions: 1. \( \lim_{x \to +\infty} f(x) = 0 \) 2. \( \lim_{x \to 0} f(x) = -\infty \) 3. \( f(5) = 0 \) 4. \( \lim_{x \to 8^-} f(x) = \infty \) 5. \( \lim_{x \to 8^+} f(x) = -\infty \)

Solution

The problem asks to find a rational function f(x)f(x) that satisfies the following conditions:

  1. limx+f(x)=0\lim_{x \to +\infty} f(x) = 0
  2. limx0f(x)=\lim_{x \to 0} f(x) = -\infty
  3. f(5)=0f(5) = 0
  4. limx8f(x)=\lim_{x \to 8^-} f(x) = \infty
  5. limx8+f(x)=\lim_{x \to 8^+} f(x) = -\infty

Step-by-step analysis of the conditions:

  1. limx+f(x)=0\lim_{x \to +\infty} f(x) = 0: This implies the function is a rational function with the degree of the denominator greater than the degree of the numerator.

  2. limx0f(x)=\lim_{x \to 0} f(x) = -\infty: This indicates there is a vertical asymptote at x=0x = 0, suggesting the denominator has xx as a factor.

  3. f(5)=0f(5) = 0: This suggests that f(x)f(x) has a root at x=5x = 5.

  4. limx8f(x)=\lim_{x \to 8^-} f(x) = \infty and limx8+f(x)=\lim_{x \to 8^+} f(x) = -\infty: This suggests there is a vertical asymptote at x=8x = 8, with different behaviors on the left and right of x=8x = 8.

Proposed function structure:

To satisfy these conditions, we need a rational function of the form: f(x)=N(x)D(x)f(x) = \frac{N(x)}{D(x)} Where N(x)N(x) is the numerator and D(x)D(x) is the denominator.

  • For the vertical asymptote at x=0x = 0, the denominator should include xx as a factor.
  • For the root at x=5x = 5, the numerator should include (x5)(x - 5).
  • For the vertical asymptote at x=8x = 8 with different behavior on either side, the denominator should include (x8)2(x - 8)^2, because the sign change between x8x \to 8^- and x8+x \to 8^+ suggests a factor of (x8)1(x - 8)^1 rather than (x8)2(x - 8)^2.

Putting this together:

A possible rational function that satisfies these conditions is: f(x)=(x5)x(x8)f(x) = \frac{(x - 5)}{x(x - 8)}

Verifying the conditions:

  1. limx+f(x)=0\lim_{x \to +\infty} f(x) = 0:

    • As x+x \to +\infty, both the numerator and denominator grow linearly, but the denominator grows faster due to the higher degree. Hence, limx+f(x)=0\lim_{x \to +\infty} f(x) = 0.
  2. limx0f(x)=\lim_{x \to 0} f(x) = -\infty:

    • As x0x \to 0, the function behaves like 1x\frac{1}{x}, which tends to -\infty.
  3. f(5)=0f(5) = 0:

    • Substituting x=5x = 5, we get f(5)=(55)5(58)=0f(5) = \frac{(5 - 5)}{5(5 - 8)} = 0.
  4. limx8f(x)=\lim_{x \to 8^-} f(x) = \infty and limx8+f(x)=\lim_{x \to 8^+} f(x) = -\infty:

    • As x8x \to 8^-, f(x)f(x) approaches ++\infty because the numerator is negative and the denominator is negative, making the overall value positive.
    • As x8+x \to 8^+, f(x)f(x) approaches -\infty because the numerator is negative and the denominator is positive, making the overall value negative.

Thus, the rational function f(x)=(x5)x(x8)f(x) = \frac{(x - 5)}{x(x - 8)} satisfies all the given conditions.

Would you like more details or have any questions? Here are some follow-up questions for deeper understanding:

  1. How do vertical asymptotes affect the behavior of rational functions?
  2. What is the role of the numerator in determining the zeros of a rational function?
  3. How can we determine the behavior of a rational function near an asymptote?
  4. What happens to a rational function as xx \to \infty based on the degrees of the numerator and denominator?
  5. How do limits help in analyzing the end behavior of functions?

Tip: Always check the degree of the numerator and denominator in rational functions to predict the end behavior (horizontal asymptotes).

Ask a new question for Free

By Image

Drop file here or Click Here to upload

Math Problem Analysis

Mathematical Concepts

Rational Functions
Limits
Asymptotes

Formulas

Rational Function f(x) = (Numerator) / (Denominator)

Theorems

Limit Theorem
Behavior at Asymptotes

Suitable Grade Level

Grades 11-12