Definitions of ellipse terms

directrix
Either line with the property that the ratio of distances from any point on the ellipse to the focus nearer the line and to the line is constant.
directrices
Plural of directrix. The two lines that have the directrix property.
eccentricity ("ek-sen-TRI-si-tee")
The constant ratio of distances from any point on the ellipse to a foucs and the directrix nearer the focus.


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