Definition
Line
A straight path with no endpoints that continues forever in both directions.
Continue from this idea into connected AXIO math.
What it means
A line never starts or stops. A page is not big enough to draw it forever, so we draw a straight stroke with an arrowhead at each end. Any two different points determine exactly one line through them.
Remember it
Two arrows mean: keep going both ways.
Example
Plot two different points, A and B. Draw the straight route through both points and add an arrowhead at each end. The result represents line AB, which continues past A in one direction and past B in the other.
Watch for
A line segment has two endpoints, and a ray has one endpoint. A line has no endpoints.
Common mix-up
The drawing looks finite because the page is finite; the two arrowheads show that the mathematical line continues.
Exact meaning
In plane geometry, a line is the unique straight one-dimensional set through any two distinct points and extends without endpoints in both directions; a drawing represents it with a finite stroke and arrowheads at both ends.