. . 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 = 1then the conic is called a parabola (ii) If this constant e < 1then the conic is called a ellipse (iii) If this constant e > 1then the conic is called a hyperbola - - Two Dimensional Analytical Geometry - II