A parabola is defined by the set of the points of the plane that are equidistant to a fixed straight line and a fixed point: $$$d(P,D)=d(P,F)$$$
Elements of the parabola
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Focus: It is the fixed point $$F$$.
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Generator line: It is the fixed straight line $$D$$.
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Parameter: The distance between the focus and the generator line of a parabola is called the parameter $$p$$.
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Axis: The straight line perpendicular to the generator that goes through the focus is called axis. It is the axis of symmetry of the parabola.
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Vertex: It is the middle point between the focus and the generator line. Also, it is possible to consider it the point of intersection of the axis with the parabola.
- Radius vector: It is the segment that joins any point of the parabola with the focus.