A conic written in polar form has eccentricity equal to 1. Which curve is it?

1. Eccentricity compares the distance to the focus with the distance to the directrix. 2. A value below 1 gives an ellipse and a value above 1 gives a hyperbola. 3. The single value e equal to 1 marks the parabola, the boundary between the two. _Source: OpenStax College Algebra (CC BY 4.0), Ch 8 "Analytic Geometry", section 8.5 Conic Sections in Polar Coordinates_