Let a B C d be the given circle, it is required to draw a square within it. Draw the diameters a b, c d, at right angles to each other; or, in other words, draw the diameter a b, and form a per-pendicular bisecting it. Then join the points a c, c b, b d, d a, and the figure a b c d is a square formed within a given circle.

Fig. 31.