Math Problem Statement

Find the constants A and B so that the graph of the function f(x) = (Ax + 9)/(33 + Bx) has x = 3 as a vertical asymptote and y = -3 as a horizontal asymptote.

Solution

To solve this problem, we need to determine the constants AA and BB such that the function

f(x)=Ax+933+Bxf(x) = \frac{Ax + 9}{33 + Bx}

has x=3x = 3 as a vertical asymptote and y=3y = -3 as a horizontal asymptote.

1. Vertical Asymptote Condition

A vertical asymptote occurs where the denominator of the function equals zero, because the function approaches infinity. Thus, to have a vertical asymptote at x=3x = 3:

33+B(3)=033 + B(3) = 0

Solving for BB:

33+3B=0    B=1133 + 3B = 0 \implies B = -11

2. Horizontal Asymptote Condition

For rational functions, the horizontal asymptote is determined by the degrees of the numerator and the denominator:

  • If the degree of the numerator equals the degree of the denominator, the horizontal asymptote is the ratio of the leading coefficients.

The degrees are the same here (both are linear, degree 1), so the horizontal asymptote is determined by:

limxf(x)=limxAx+933+Bx=AB\lim_{x \to \infty} f(x) = \lim_{x \to \infty} \frac{Ax + 9}{33 + Bx} = \frac{A}{B}

We are given that the horizontal asymptote is y=3y = -3, so:

AB=3\frac{A}{B} = -3

Given that B=11B = -11 from the vertical asymptote condition, we substitute it into the equation:

A11=3    A=33\frac{A}{-11} = -3 \implies A = 33

Final Values

Thus, the constants are:

A=33,B=11A = 33, \quad B = -11

Would you like further details or have any questions?

Related Questions:

  1. How would the function change if the vertical asymptote was at x=5x = 5?
  2. What if the horizontal asymptote was y=2y = 2?
  3. How does the function behave near its vertical asymptote?
  4. Can you explain why the degrees of the numerator and denominator matter for horizontal asymptotes?
  5. How would the function be altered if the numerator was quadratic?

Tip:

For horizontal asymptotes, always check the relative degrees of the numerator and denominator—it helps determine the end behavior of the function.

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Math Problem Analysis

Mathematical Concepts

Rational Functions
Asymptotes

Formulas

Vertical Asymptote: Denominator equals zero
Horizontal Asymptote: Leading coefficient ratio for same degree polynomials

Theorems

Horizontal and Vertical Asymptote Rules for Rational Functions

Suitable Grade Level

Grades 10-12