Editing Perpendicular (section)

===Parabolas===

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 [[Parabola#Intersection of a tangent and perpendicular from focus|other tangent line to the parabola]] is perpendicular to the line from that point through the parabola's [[focus (geometry)|focus]].

The [[Parabola#Orthoptic property|orthoptic property]] of a parabola is that If two tangents to the parabola are perpendicular to each other, then they intersect on the directrix. Conversely, two tangents which intersect on the directrix are perpendicular. This implies that, seen from any point on its directrix, any parabola subtends a right angle.