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An ellipse, its minimum bounding box, and its director circle. In geometry, the director circle of an ellipse or hyperbola (also called the orthoptic circle or Fermat–Apollonius circle) is a circle consisting of all points where two perpendicular tangent lines to the ellipse or hyperbola cross each other.
Let the perpendicular to the line of symmetry, through the focus, intersect the parabola at a point T. Then (1) the distance from F to T is 2f, and (2) a tangent to the parabola at point T intersects the line of symmetry at a 45° angle. [13]: 26 Perpendicular tangents intersect on the directrix
But only a tangent line is perpendicular to the radial line. Hence, the two lines from P and passing through T 1 and T 2 are tangent to the circle C. Another method to construct the tangent lines to a point P external to the circle using only a straightedge: Draw any three different lines through the given point P that intersect the circle twice.
In a parabola, the axis of symmetry is perpendicular to each of the latus rectum, the directrix, and the tangent line at the point where the axis intersects the parabola. From a point on the tangent line to a parabola's vertex, the other tangent line to the parabola is perpendicular to the line from that point through the parabola's focus.
A particular tangent line distinguishes the hyperbola from the other conic sections. [18] Let f be the distance from the vertex V (on both the hyperbola and its axis through the two foci) to the nearer focus. Then the distance, along a line perpendicular to that axis, from that focus to a point P on the hyperbola is greater than 2f. The tangent ...
The line perpendicular to the tangent line to a curve at the point of tangency is called the normal line to the curve at that point. The slopes of perpendicular lines have product −1, so if the equation of the curve is y = f(x) then slope of the normal line is /
Because the tangent line is perpendicular to the normal, an equivalent statement is that the tangent is the external angle bisector of the lines to the foci (see diagram). Let L {\displaystyle L} be the point on the line P F 2 ¯ {\displaystyle {\overline {PF_{2}}}} with distance 2 a {\displaystyle 2a} to the focus F 2 {\displaystyle F_{2 ...
Conversely, at any point R on the curve C, let T be the tangent line at that point R; then there is a unique point X on the tangent T which forms with the pedal point P a line perpendicular to the tangent T (for the special case when the fixed point P lies on the tangent T, the points X and P coincide) – the pedal curve is the set of such ...