Question

How do you know when a limit has a vertical asymptote?

Answer 1

When it get's closer and closer to a number without actually hitting it

Answer 2

Generally, the x domain would be affected by a vertical asymptote (unless for some reason, the y axis is horizontal). For there to be an asymptote, there must be some value that cannot be reached, but can be bordered very closely. Since this is a vertical asymptote, that means there is some x value that produces an undefined y value, such as 1/x, where the vertical asymptote would be the line x=0.