


The Coordinate Plane
The coordinate plane is a plane determined by two perpendicular
lines, the xaxis and the yaxis.
The xaxis is the horizontal axis, and the yaxis
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 yaxes 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 xcoordinate.
The xcoordinate is the point’s location along
the xaxis and can be determined by the point’s
distance from the yaxis (where x =
0). If the point is to the right of the yaxis,
its xcoordinate is positive, and if the point
is to the left of the yaxis, its xcoordinate
is negative. The second coordinate in a coordinate pair is the ycoordinate.
The ycoordinate of a point is its location along
the yaxis and can be calculated as the distance
from that point to the xaxis. If the point is
above the xaxis, its ycoordinate
is positive, and if the point is below the xaxis,
its ycoordinate is negative.
The Quadrants
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 xcoordinate that is 4 units to the right of
the yaxis and a ycoordinate
that is 2 units below the xaxis. This is how the
coordinates of a point specify its exact location. The coordinates
of the origin are, by definition, (0, 0).
