Which of the following is an example of an undefined notion?

Question

a. A line is an example of an undefined notion
b. An angle is an example of an undefined notion
c. A line segment is an example of an undefined notion
d. A circle is an undefined notion

Answer 1

The correct answer is:

a. A line is an example of an undefined notion.

In geometry, certain concepts such as "point," "line," and "plane" are considered undefined notions. These terms do not have formal definitions but are understood through their properties and relationships with other concepts.