Number Lines 0 20 Printable
A number line is usually interpreted as horizontal but the vertical axis (y-axis) is also a number line in a Cartesian coordinate plane. Positive numbers are always on the right side of zero according to one convention, negative numbers are always on the left side of zero, and arrowheads on both ends of the line are intended to indicate that the line continues forever in both positive and negative directions. Another convention only uses one arrowhead that shows the direction in which numbers are rising. The line continues in the positive and negative directions indefinitely according to the geometry rules that characterize a line without endpoints as an infinite line, a line with one endpoint as a ray, and a line with two endpoints as a line section.