Conics

Conics

Definition

A conic is the locus of a point which moves in a plane, so that its distance from a fixed point bears a constant ratio to its distance from a fixed line not containing the fixed point.

The fixed point is called focus, the fixed line is called directrix and the constant ratio is called eccentricity, which is denoted by e.

(i) If this constant e = 1 then the conic is called a parabola

(ii) If this constant e < 1 then the conic is called a ellipse

(iii) If this constant e > 1 then the conic is called a hyperbola