Final answer:
A horizontal asymptote is located by comparing the degrees of the numerator and denominator of a rational function. If the degrees are equal, it's the ratio of the leading coefficients; if the numerator's degree is less, it's y = 0; and if it's greater, there typically isn't one.
Step-by-step explanation:
To locate a horizontal asymptote for a function, you generally compare the degrees of the numerator and denominator in a rational function. If the degrees are equal, the horizontal asymptote is y = the ratio of the leading coefficients. If the degree of the numerator is less than the degree of the denominator, the horizontal asymptote is y = 0. If the degree of the numerator is greater, there is no horizontal asymptote; instead, there might be an oblique or no asymptote at all.
For example, consider the function y = 1/x mentioned in the provided information. Since the degree of the numerator (0, since there is no x term in the numerator) is less than the degree of the denominator (1), the horizontal asymptote is y = 0. Similarly, for a linear equation like y = 3x + 9, which is the equation of a straight line with a slope (m) of 3 and a y-intercept (b) of 9, there are no horizontal asymptotes because linear functions continue to increase or decrease without approaching a constant value.