12.5.6 Perpendicular lines and planes in space: perpendicular
See section 11.7.6 for perpendicular lines in the plane.
The perpendicular command returns and draws a line or plane,
depending on the arguments. The possible arguments are:
A point A and a line L.
perpendicular(A,L) returns and draws the line through
A that is perpendicular to L.
- A line L and a plane P.
perpendicular(L,P) returns and draws the plane containing
L that is perpendicular to P.