If #x=a# is a vertical asymptote of a function #f(x)#, then it means that the graph of #f# displays a "blowing-up" or a "Blowing-down" behavior there, that is, either the left-hand limit or the right-hand limit (or both) must be an infinite limit.
#lim_{x to a^-}f(x)=pm infty# or #lim_{x to a^+}f(x)=pm infty#