The horizontal asymptote of a rational function tells us the limiting value of that function as it approaches infinity.
For a rational function to have a horizontal asymptote of

then,
![<b>the highest degree of x in the numerator must be equal to the highest degree of x in the denominator.</b>]()
The second condition is that,
![<b>the coefficient of the highest degree in the numerator and the coefficient of the highest degree in the denominator should be in the ratio 2:9.</b>]()
Example are given in the graph above.
Here are some other examples,

