For 10 points, name these imaginary lines which functions approach but do not cross.
On a phase portrait, the eigenvectors serve as these, and spiral points may be stable with respect to them. These act as essential discontinuities, in contrast with "removable" and "jump" discontinuities. Their slope equals plus or minus b over a for a hyperbola in standard form. The graph of the arctangent x or of a logistic curve will have two of these. "Oblique" or "slant" ones occur when the degree of the numerator of a rational function is greater than the degree of the denominator. The limit of a function as x goes to infinity or negative infinity is the "horizontal" one. For 10 points, name these imaginary lines which functions approach but do not cross.
On a phase portrait, the eigenvectors serve as these, and spiral points may be stable with respect to them.
asymptotes [or vertical asymptotes; or horizontal asymptotes; or slant asymptotes; or oblique asymptotes]