11.CONIC SECTION

Curves obtained by slicing a cone by a plane that doesn't pass through vertex are called  conic section or conics. 
A Conic is the locus of point such that the ratio of  its distance  from fixed point to its distance from a fixed line is a constant. 
The fixed point is called the focus and fixed line is called directrix and fixed  ratio is called  eccentricity (e)
If e=1    PARABOLA
   e<1    ELLIPSE
   e>1       HYPERBOLA
   e=0    CIRCLE 

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