Let a b c be a circle; it is required to draw within it a triangle whose sides are equal to one another. Commencing from any point a, mark on the circumference of the circle a series of spaces equal to the radius of the circle, of which there will be six, and draw the arcs a d d b, etc. Then join every alternate point as a b, b c, c a, and the several lines will together form an equilateral triangle.