นิพจน์ 3: "y" squared equals StartFraction, distance left parenthesis, left parenthesis, "x" , "y" , right parenthesis , "F" , right parenthesis squared Over "e" squared , EndFractiony2=distancex,y,F2e2c
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The distance ratio, e_c, is also called the "eccentricity". For parabolas, it's 1, for hyperbolas, it's greater than one, and for ellipses, it's between zero and one.