The Coordinate Plane
The coordinate plane is a plane determined by two perpendicular
lines, the x-axis and the y-axis.
The x-axis is the horizontal axis, and the y-axis
is the vertical axis. Every point in the plane can be stated by
a pair of coordinates that express the location of the point in
terms of the two axes. The intersection of the x-
and y-axes is designated as the origin, and its
point is (0, 0).
As you can see from the figure, each of the points on
the coordinate plane is expressed by a pair of coordinates: (x, y).
The first coordinate in a coordinate pair is called the x-coordinate.
The x-coordinate is the point’s location along
the x-axis and can be determined by the point’s
distance from the y-axis (where x =
0). If the point is to the right of the y-axis,
its x-coordinate is positive, and if the point
is to the left of the y-axis, its x-coordinate
is negative. The second coordinate in a coordinate pair is the y-coordinate.
The y-coordinate of a point is its location along
the y-axis and can be calculated as the distance
from that point to the x-axis. If the point is
above the x-axis, its y-coordinate
is positive, and if the point is below the x-axis,
its y-coordinate is negative.
The coordinate plane is divided into four quadrants. Each
quadrant is a specific region in the coordinate plane. The region
in which x > 0 and y > 0 is Quadrant
I. The region in which x < 0 and y >
0 is Quadrant II. The region in which x < 0
and y < 0 is Quadrant III. The region in which x >
0 and y < 0 is Quadrant IV.
For example, the point (4, –2) lies in quadrant IV, with
an x-coordinate that is 4 units to the right of
the y-axis and a y-coordinate
that is 2 units below the x-axis. This is how the
coordinates of a point specify its exact location. The coordinates
of the origin are, by definition, (0, 0).