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What Are The Undefined Terms Of Geometry?

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Arianna Vaccaro Profile
Arianna Vaccaro answered
The three undefined terms in Geometry include the following:

• Point: The reason a point is undefined is because it has no actual fixed size or dimensions. When referring to a point on a map for example, it is usually given a name of a capital letter such as X or Y.
• Line: When referring to a line in geometry, it has no thickness and it can be extended in either horizontal direction by any length. It can be defined as a straight line that has two arrowheads on each side. This means it can be extended out at either side to any length at all. These are usually given a small non-capital letter as a name such as x or y.
• Plane: This is usually shape that can be similar to a wall or a table top. It is described as being undefined as it has no boundaries and can be extended in all directions. There is no limit to how far it can be extended.
All of the above can be subject to change and are not based on specific facts. They are used to base other work and theories on, so that is why they are often referred to as being 'undefined.'
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Anonymous answered


A point is like a star in the night sky.   It is a little spec in a large endless sky.   However, unlike starts, geometric points have no size.   Think of them as being so small that they take up zero amount of space.



A line is like the edge of a ruler, that never ends.   Take a ruler and draw a line - now imagine if that line kept going straight forever.   The line you have is thick enough for you to see, but you need to imagine that your line is so thin that you can't see it - it has no thickness at all.   That is a geometric line.



A plane is a flat piece of land (like a football field) that extends forever.   Imagine that you can pick that football field up, and put it anywhere in the air that you like.   You can even turn it side ways, or diagonally.   A plane is just a flat edge (like a piece of paper) that has no thickness (just like the line) and extends forever.

:] -mAtt
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Anonymous answered
Point, line and plane
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Anonymous answered
The Undefined Terms in Geometry

The 3 "undefined terms in geometry" are the building blocks for the rest of the subject.  They are like the big cinder blocks that are first placed at the bottom of a house - without those clocks, the rest of the house couldn't be built.

The 3 terms are point, line, and plane.  Do not be intimidated by the the phrase "undefined."  You may already know a pretty good definition for these terms, especially the first two.

NEW!  For an exciting, interactive way to learn about the undefined terms in geometry, please take a look at our Geometer's Sketchpad Tutorial.

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