GRAPHING
Algebra
The use of a graph starts with the plotting of data points using the coordinate system. These data
points are known as the abscissa and the ordinate.
The abscissa, also known as the
y-coordinate, is the distance along the y-axis. The ordinate, also known as the x-coordinate, is
the distance along the x-axis. A point on a Cartesian coordinate graph is specified by giving its
x-coordinate and its y-coordinate. Positive values of the x-coordinate are measured to the right,
negative values to the left. Positive values of the y-coordinate are measured up, negative values
down. For example, the x- and y-coordinates are both zero at the origin. The origin is denoted
as (0,0), where the first zero refers to the value of the x-coordinate. Point A in Figure 1 is
denoted as (0,4), since the value of the x-coordinate is zero, and the value of the y-coordinate
is 4. In Quadrant I, every point has a positive x-coordinate and a positive y-coordinate. Point
B in Figure 1 is located in Quadrant I and is denoted by (4,2). Fractional values of coordinates
can also be shown. Point C in Figure 1 is denoted by (1,1.5). In Quadrant II, every point has
a negative x-coordinate and a positive y-coordinate. Point D is denoted by (-2,2). In Quadrant
III, every point has a negative x-coordinate and a negative y-coordinate. Point E is located in
Quadrant III and is denoted by (-2,-4). In Quadrant IV, every point has a positive x-coordinate,
but a negative y-coordinate. Point F is located in Quadrant IV and is denoted by (5,-4).
Cartesian Coordinate Graphs
The most common type of graph using the Cartesian Coordinate System is one in which all
values of both the x-coordinate and the y-coordinate are positive. This corresponds to Quadrant
I of a Cartesian coordinate graph. The relationship between two physical quantities is often
shown on this type of rectangular plot. The x-axis and the y-axis must first be labeled to
correspond to one of the physical quantities. The units of measurement along each axis must also
be established. For example, to show the relationship between reactor power level and time, the
x-axis can be used for time in minutes and the y-axis for the reactor power level as a percentage
of full power level. Data points are plotted using the associated values of the two physical
quantities.
Example: The temperature of water flowing in a high pressure line was measured at regular
intervals. Plot the following recorded data on a Cartesian coordinate graph.
Time (min)
Temperature (°F)
0
400°
15
420°
30
440°
45
460°
60
480°
75
497°
90
497°
105
497°
120
497°
MA-02
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