Rational Functions and Models

1. Rational Functions and Models 4.6 Identify a rational function and state its domain Identify asymptotes Interpret asymptotes Graph a rational function by using transformations Graph a rational function by hand (optional)

2. Rational Function A function f represented by where p(x) and q(x) are polynomials and q(x) ≠ 0, is a rational function.

3. Vertical Asymptotes The line x = k is a vertical asymptote of the graph of f if f(x) g ∞ or f(x) g –∞ as x approaches k from either the left or the right.

4. Horizontal Asymptotes The line y = b is a horizontal asymptote of the graph of f if f(x) gb as x approaches either ∞ or –∞.

5. Finding Vertical & Horizontal Asymptotes Let f be a rational function given by written in lowest terms. Vertical Asymptote To find a vertical asymptote, set the denominator, q(x), equal to 0 and solve. If k is azero of q(x), then x = k is a vertical asymptote. Caution: If k is a zero of both q(x) andp(x), then f(x) is not written in lowest terms, and x – k is a common factor.

6. Finding Vertical & Horizontal Asymptotes Horizontal Asymptote (a)If n<m the degree of the numerator is less than the degree of the denominator, then y = 0(the x-axis) is a horizontal asymptote. (b)If n=mthe degree of the numerator equals the degree of the denominator, then y = a/b isa horizontal asymptote, where a is the leading coefficient of the numerator and bis the leading coefficient of the denominator. (c)If n>m the degree of the numerator is greater than the degree of the denominator, thenthere are no horizontal asymptotes.

7. Since the domain is Teaching Example 1 • Determine if the function is rational and state its domain. (b) (a) Solution (a) Both the numerator and the denominator are polynomials, so the function is rational. The numerator is not a polynomial, so the function is not rational. Since the domain is all real numbers.

8. (a) (b) (c) Teaching Example 4 • Determine any horizontal or vertical asymptotes for each rational function.

9. Since the degrees of the numerator and the denominator are both 1, and the ratio of the leading coefficients is , the horizontal asymptote is is the vertical asymptote. Teaching Example 4 (continued) Solution (a) To find the vertical asymptote, solve 1 − 2x = 0.

10. Teaching Example 4 (continued)

11. (b) To find the vertical asymptotes, solve are the vertical asymptotes. Teaching Example 4 (continued) The degree of the numerator is one less than the degree of the denominator, so the x-axis (y = 0) is the horizontal asymptote.

12. Teaching Example 4 (continued)

13. (c) Teaching Example 4 (continued) The degree of the numerator is greater than the degree of the denominator, so there are no horizontal asymptotes. When x = 2, both numerator and denominator equal 0, so the expression is not in lowest terms.

14. Teaching Example 4 (continued) The graph of h(x) is the line y = x + 2 with the point (2, 4) missing. There are no vertical asymptotes.

15. The graph of shifted two units left and one unit down. Teaching Example 6 • Graph Solution

16. The graph of has horizontal asymptote y = 0 and vertical asymptotex = 0. Teaching Example 7 • Use the graph of to sketch a graph of • Write g(x) in terms of f(x). Solution

17. Teaching Example 7 (continued) • The graph of g(x) is the graph of f(x) shifted one unit left and one unit down.

18. Since the degrees of the numerator and the denominator are the same, and the ratio of the leading coefficients is , the horizontal asymptote is Teaching Example 9 Solution

19. is the horizontal asymptote. Since x ≠ −2, there is a hole in the graph at Teaching Example 9 (continued) • When x = −2, both numerator and denominator equal 0, so the expression is not in lowest terms.

20. Teaching Example 9 (continued)

21. Teaching Example 11 Use these steps to graph this polynomial by hand: Make the the function is rational and in simplest form. Find any Asymptotes (Vertical, Horizontal or Oblique) Find y-intercept (if any) Find x-intercept (if any) Determine if the graph will intersect the H.A.(or oblique) Plot selected points Complete the graph.

22. Teaching Example 11 (continued)