11. What is the altitude of a rectilineal figure?
12. If two triangles have equal altitudes, how do their areas vary?
13. How do these areas vary if they have equal bases but unequal altitudes?
14. If both bases and altitudes differ, how do the areas vary?
15. When are two lines divided proportionally?
16. If in two lines divided proportionally a pair of homologous points coincide with their point of intersection, what property holds for the lines joining the other pairs of homologous points?
17. Define reciprocal proportion.
18. If two triangles have equal areas, prove that their perpendiculars are reciprocally proportional to the bases.
19. What is meant by figures inversely similar?
20. If two figures be inversely similar, how can they be changed into figures directly similar?