| 21. | Measured along the axis of symmetry, the vertex, A, is equidistant from the focus, F, and from the directrix.
|
| 22. | The ellipse thus generated has its second focus at the center of the directrix circle, and the ellipse lies entirely within the circle.
|
| 23. | It follows that the magnitude of the tension at a point is, which is proportional to the distance between the point and the directrix.
|
| 24. | In an ellipse, the semi-minor axis is the geometric mean of the maximum and minimum distances of the ellipse from a directrix.
|
| 25. | Correspondingly, since C is on the directrix, the-coordinates of F and C are equal in absolute value and opposite in sign.
|
| 26. | Point P is called the pole of the neusis, line l the directrix, or guiding line, and line m the catch line.
|
| 27. | As shown first by Apollonius of Perga, a hyperbola can be used to directrix and "'B "'as a focus.
|
| 28. | The orthoptic property of a parabola is that If two tangents to the parabola are perpendicular to each other, then they intersect on the directrix.
|
| 29. | It is also possible to describe all the conic sections as loci of points that are equidistant from a single focus and a single, circular directrix.
|
| 30. | *It cannot be a rotated parabola with A as the focus and y = 2x as the directrix because AB is a ( straight ) line segment.
|
