straight line
The straight line (line) is kind of the curve that is the geometric object which does not have thickness and it lengthens straight endlessly forever and does not have an endpoint.
There is a half line (ray, half-line) which lengthened straight in a similar object endlessly as an initial point at the endpoint of (goddamn, line segment, segment which I do not do it) for a line and the one to have length and both ends toward of the limitedness.
By the geometry of Euclid, the straight line is a no definition technical term essentially.
In other words I do it when I satisfy relations (an axiom / a postulate) that there is merely and develop a theory without defining it directly "what the straight line is".
It is the following things in Euclidean geometry：
In addition, for example, the following things are led by such an axiom： Two different straight lines share one point at most.
Two different planes share one straight line at most.
A straight line and the segment of a line do not have a direction, and the half line is usually treated as a thing having a direction.
For example, it is AB = BA when it writes a segment of a line which links B to two points of A as AB.
I think about the thing called a, on the other hand, kept straight line, segment of a line suitable for and the half line which do not have a direction.
For example, I distinguish an initial point for the line and a terminal and call the thing which thought about a direction to a segment of a line with a directed segment of a line and think for a directed segment of a line with AB ≠ BA.
There is a half line (ray, half-line) which lengthened straight in a similar object endlessly as an initial point at the endpoint of (goddamn, line segment, segment which I do not do it) for a line and the one to have length and both ends toward of the limitedness.
By the geometry of Euclid, the straight line is a no definition technical term essentially.
In other words I do it when I satisfy relations (an axiom / a postulate) that there is merely and develop a theory without defining it directly "what the straight line is".
It is the following things in Euclidean geometry：
In addition, for example, the following things are led by such an axiom： Two different straight lines share one point at most.
Two different planes share one straight line at most.
A straight line and the segment of a line do not have a direction, and the half line is usually treated as a thing having a direction.
For example, it is AB = BA when it writes a segment of a line which links B to two points of A as AB.
I think about the thing called a, on the other hand, kept straight line, segment of a line suitable for and the half line which do not have a direction.
For example, I distinguish an initial point for the line and a terminal and call the thing which thought about a direction to a segment of a line with a directed segment of a line and think for a directed segment of a line with AB ≠ BA.