[Illustration: _Fig. 1_]
A, B, is the given right line. From the point C, with a radius longer
than the perpendicular distance describe the arc, or part of a circle,
D, D. And from the points of intersection with the right line A, B,
describe arcs cutting each other at C and E. Join C and E, and the
perpendicular is obtained on either side of the right line A, B.