8. What is a regular polygon?
9. What figures can be inscribed in, and circumscribed about, a circle by means of Book IV.?
10. What regular polygons has Gauss proved to be inscriptable by the line and circle?
11. What is meant by escribed circles?
12. How many circles can be described to touch three lines forming a triangle?
13. What is the centroid of a triangle?
14. What is the orthocentre?
15. What is the circumcentre?
16. What is the polar circle?
17. When is the polar circle imaginary?