asymptote
A line a graph approaches but (usually) never crosses near a bad point or at infinity.
An asymptote is a line that a graph gets arbitrarily close to without (typically) touching it. A vertical asymptote occurs where a rational function's denominator hits zero and the numerator doesn't; horizontal and slant asymptotes describe the graph's behavior as x \to \pm\infty.
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Examples
f(x) = \frac{1}{x-2} has a vertical asymptote at x=2 and a horizontal asymptote at y=0.
See also
Point table
Graph settings
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