GEOMETRY OF CONICS.
INTRODUCTION.
A Conic is a curve traced by a point which moves in a plane containing a fixed point and a fixed straight line, in such a way that its distance from the fixed point is in a constant ratio to its perpendicular distance from the fixed straight line.
The fixed point is called the Focus.
The fixed straight line is called the Directrix.
The constant ratio is called the Eccentricity, and is usually represented by the letter e.
When the eccentricity is equal to unity, the Conic is called a Parabola (e = 1).
When the eccentricity is less than unity, the Conic is called an Ellipse (e < 1).
When the eccentricity is greater than unity, the Conic is called a Hyperbola (e > 1).
The straight line drawn through the focus perpendicular to the directrix is called the Axis of the Conic.
The point (or points) in which the axis intersects the Conic is called the Vertex.
The Conics are so called from the circumstance that they are, and were originally studied as, the plane sections of the surface
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