Problem: In connection with proof in geometry, indicate which one of the following statements is incorrect:
Answer Choices:
A. Some statements are accepted without being proved.
B. In some instances there is more than one correct order in proving certain propositions.
C. Every term used in a proof must have been defined previously.
D. It is impossible to have a correct conclusion if in the beginning an incorrect proposition is introduced followed by correct reasoning.
E. Indirect proof can be used whenever there are two or more contrary propositions.
Solution:
(C) is incorrect since some terms (primitives) must necessarily remain undefined.