X coordinate

The x-coordinate is a number that describes the horizontal position of a point in terms of distance and direction along the x-axis. While the orientation of the 2D rectangular coordinate plane can theoretically differ, it almost never does, so a negative x-coordinate typically indicates that a point lies left of the origin, and a positive number indicates that a point lies to the right of the origin.

The x-coordinate is the first number in both an ordered pair (x, y) and ordered triple (x, y, z) in a 2D rectangular coordinate plane (shown below) and a 3D coordinate plane, respectively.

The x-coordinates for points A and B, shown in the coordinate plane above, are 2 and -4, respectively.

Measuring horizontal distance

The length of a horizontal line segment can be determined by taking the absolute value of the difference between the x-coordinates of its endpoints.

While you can count 6 units along the x-axis from one endpoint to the other to determine the length of the line segment graphed above, it can be more efficient to take the absolute value of the difference (particularly with larger distances): |2 - (-4)| = |6| = 6 units or |-4 - 2| = |-2| = 6 units.

Did you know?

Although it is not used much anymore, the x-coordinate of a point is also referred to as the abscissa (the y-coordinate is referred to as the ordinate).

The abscissa of a point describes its horizontal position relative to the origin or y-axis. If the abscissa is positive, as in the figure above, it is right of the origin or y-axis. If it is negative, as in the figure below, it is left of the origin or y-axis. In the above figure, the abscissa is 4 units right (+4) of the origin or y-axis, and in the figure below, it is 4 units left (-4) of the origin or y-axis