Proof: By Euclid
(related to Proposition: Prop. 11.12: Construction of Straight Line Perpendicular to Plane from point on Plane)
- Let the given plane be the reference (plane), and $A$ a point in it.
- So, it is required to set up a straight line at "right angles" to the reference plane at point $A$.
Adapted from (subject to copyright, with kind permission)
- Fitzpatrick, Richard: Euclid's "Elements of Geometry"