A regular polygon has all its sides equal, and all its angles of an equal opening. When such a polygon is inscribed in a circle, the sides are cords of equal arcs, and the points cut the circle into equal parts.
26. Inscribe a regular octagon in a circle. (fig. 16.)
Draw two diameters perpendicular to each other, then divide each quarter of the circle into halves by other diameters ; then draw arcs from diameter to di- ameter.
27. Inscribe a regular pentagon in a circle. (fig. 17.)
It is difficult by the eye alone to divide the circum- ference into five equal parts, and the object of this problem is to exercise the pupils.
28. Make a triangle, and circumscribe a circle.
First make a triangle, and then the object is to de- scribe a circle which shall cut each of its three points. To do this, raise a perpendicular on the middle of one
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(fig. 18.)
