[Illustration: _Fig. 4_]
Take the radius of the circle, and with it mark off six points on the
circumference. Take two of these lengths of the radius and join their
extreme points A and B, which will be the base. Now take this base as a
radius and describe alternately two arcs cutting each other at C. Join
A, C, and B, C, and a triangle is formed, whose sides being equal is
termed an _equilateral triangle_.
In order to ensure its being upright, erect a perpendicular at the
centre, and let the two sides A, C, and B, C, meet that perpendicular
where it intersects the circumferences. Or, begin the triangle at this
point, and mark off two lengths of the radius, joining the extreme
points as before; and do this at each side of the perpendicular;
finally connecting the distant extremities of the two sides for a base.