"Defined items" are defined in terms of "undefined terms".
they are not defined
A term that is undefined mean simply that it is not defined. The prefix un means not, and if you add it to the word defined, ta da, you get undefined.
It is a very basic concept which cannot be defined. Undefined terms are used to define other concepts. In Euclidean geometry, for example, point, line and plane are not defined.
The difference between defined and undefined terms is that the defined terms can be combined with each other and with undefined terms to define still more terms. These are undefined terms: 1.plane 2.point 3.line These are defined terms: 1.ray 2.union of sets 3.space 4.subset 5.set 6.proper subset 7.opposite rays 8.postulate 9.betweenness of points 10.bisector of a segment 11.midpoint of a segment 12.line segment 13.lenght of a segment 14.collinear points 15.complement of a set 16.coplanar points 17.disjoint sets 18.element 19.empy set 20.finite set 21.geometry 22.infinite set 23.intersection of sets
The three undefined terms are the point,the line and the plane.
The answer depends on which undefined terms the question refers to.
the three terms; point, line and plane can be defined although it is called the undefined terms still we know and we can define the meanings of that terms.. common sense? joke.
This is true not just in geometry but in every field of knowledge. You can define complicated concepts in terms of simpler ones, and those simpler ones in still simpler ones and so on. However, you will end up with a few terms which cannot be defined in terms of simpler concepts (without going into a circular definition). These terms must remain undefined.
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physical representation of undefined terms in real life?
Points, lines and planes are precisely defined terms. These concepts have to be clearly delineated to form fundamental planks in geometry, and that's because as they do. In suggesting that they are undefined, we'd have to suspect everything that was built on them. No geometric figure could be discussed with any certainty unless the elements that make it up are clearly defined and understood.