Recall the definition of the horizontal asymptote:
The line y = b {\displaystyle y=b} is the horizontal asymptote of the function y = f ( x ) {\displaystyle y=f(x)} if lim x → ∞ f ( x ) = b {\displaystyle {\underset {x\to \infty }{\lim }}f(x)=b} or lim x → − ∞ f ( x ) = b {\displaystyle {\underset {x\to -\infty }{\lim }}f(x)=b} .
