The Cartesian Coordinate Plane
 It is vitally important that a person be able to read
graphs. Lots of information is presented in newspapers
and other reports in graphical form. Some of the most
common types of graphs to be used are bar graphs, pie
charts, and line graphs.
– Bar graphs
– Pie charts (circle graphs)
– Line graphs.
 The system used in most mathematics for graphing is
called the “Cartesian” (or Rectangular)
coordinate plane.
– The plane consists of a vertical axis
and a horizontal axis. (Plural for axis is “axes”.)
Each axis is a number line. The lines are perpendicular to each
other and cross each other at 0.
– The origin is the point where the two
lines cross.
– The position of a point in the coordinate plane is
given by an ordered pair (socalled because
order is important).
 The first coordinate gives the horizontal position of the
point. When unknown, this is usually (but not always)
represented by x.
 The second coordinate gives the vertical position of the
point. When unknown, this is usually (but not always)
represented by y . Plot some points and read
coord’s, then give ordered pairs and plot the
points.
 Stay away from locking yourself into thinking x and y .
– The coordinate plane is broken into 4 quadrants,
starting in the upper right and moving counterclockwise around
the origin.
Quadrant I is where both coordinates are
positive.
Quadrant II is where the first coordinate is
negative and the second coordinate is positive.
Quadrant III is where both coordinates are
negative.
Quadrant IV is where the first coordinate is
positive and the second coordinate is negative.
