22. What propositions in Book I. are the obverse respectively of Propositions iv., v., vi., xxvii.?
23. What proposition is an instance of the rule of identity?
24. What are congruent figures?
25. What other name is applied to them? Ans. They are said to be identically equal.
26. Mention all the instances of equality which are not congruence that occur in Book I.
27. What is the difference between the symbols denoting congruence and identity?
28. Classify the properties of triangles and parallelograms proved in Book I.
29. What proposition is the converse of Prop. xxvi., Part I.?
30. Define adjacent, exterior, interior, alternate angles respectively.
31. What is meant by the projection of one line on another?