curve

the trace of a point whose direction of motion changes. There is no better example of this than the work done by the ancient Greeks on the

conic section

circle
**curves**known as the conics: the ellipse, the parabola, and the hyperbola.conic section

(geometry) a curve generated by the intersection of a plane and a circular cone

ellipse in which the two axes are of equal length

His work "Conics" was the first to show how all three curves, along with the

**circle**, could be obtained by slicing the same right circular cone at continuously varying angles.

hyperbola

an open curve formed by a plane that cuts the base of a right circular cone

parabola

a curve formed by an object thrown in the air and falling

ellipse

a closed plane curve with an oval shape

**center**: the point (

*h*,

*k*) at the center of a circle, an ellipse, or an hyperbola.

**vertex**(VUR-teks): in the case of a parabola, the point (

*h*,

*k*) at the "end" of a parabola; in the case of an ellipse, an end of the major axis; in the case of an hyperbola, the turning point of a branch of an hyperbola; the plural form is "vertices" (VUR-tuh-seez).

**focus**(FOH-kuss): a point from which distances are measured in forming a conic; a point at which these distance-lines converge, or "focus"; the plural form is "foci" (FOH-siy).

**directrix**(dih-RECK-triks): a line from which distances are measured in forming a conic; the plural form is "directrices" (dih-RECK-trih-seez).

**axis**(AK-siss): a line perpendicular to the directrix passing through the vertex of a parabola; also called the "axis of symmetry"; the plural form is "axes" (ACK-seez).

**major axis:**a line segment perpendicular to the directrix of an ellipse and passing through the foci; the line segment terminates on the ellipse at either end; also called the "principal axis of symmetry"; the half of the major axis between the center and the vertex is the semi-major axis.

**minor axis:**a line segment perpendicular to and bisecting the major axis of an ellipse; the segment terminates on the ellipse at either end; the half of the minor axis between the center and the ellipse is the semi-minor axis.

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