Vertical Asymptote of a Graph A line x = a is a vertical asymptote of the graph of a function y = f(x) if either lim f(x) = two or lim f(x) = too. Example 2B: Find the vertical asymptote(s) of each function. a. f(x)=X+x-6 b. g(x) = 5-3x x -9 x-1