Illustration showing angles formed by two secants, two tangents, or a tangent and a secant, drawn to…

Illustration to let fall a perpendicular upon a given line from a given external point.

Illustration showing that tangents drawn at the ends of any diameter are parallel to each other.

Illustration of how to draw a tangent to an ellipse from an external point.

Illustration showing the tangents drawn at two corresponding points of an ellipse and its auxiliary…

Illustration showing that the perpendicular is the shortest line that can be drawn to a straight line…

Illustration showing only one perpendicular can be drawn to a given line from a given external point.