This question involves a graph, but, unfortunately, I have no means of reproducing it. I shall try my utmost to describe it, or rather the section of it that confounds me. Consider the function f. For what values of x_0 does the lim x-->x_0 f(x) exist, where -9<= x_0 <=4? The answer says that at the value x_0 = -6 the limit does not exist (d.n.e.), but I think the limit is positive infinity and don't know why it d.n.e. Here is the description: f(-6) = 3, so there is a black point at (-6,3). Now as x approaches -6 from the left side, the curve goes upward, or without bound (+infinity). As x approaches -6 from the right side, there is another curve that goes upward, or without bound (+infinity), so it seems like there is a vertical asymptote at x_0 = -6 (but a point exists at -6). This is the section that baffles me. If you need a clearer description, I shall try to do my best. Thanks.