A conic written in polar form has eccentricity equal to 1. Which curve is it?
- An ellipse
- A hyperbola
- A circle
- A parabola
Show answer and solution
Correct answer: D. A parabola
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_