Unformatted text preview: P below on the left. To use the numbers on the axes to label this
point, we imagine dropping a vertical line from the xaxis to P and extending a horizontal line
from the y axis to P . We then describe the point P using the ordered pair (2, −4). The ﬁrst
number in the ordered pair is called the abscissa or xcoordinate and the second is called the
ordinate or y coordinate.3 Taken together, the ordered pair (2, −4) comprise the Cartesian
coordinates of the point P . In practice, the distinction between a point and its coordinates is
blurred; for example, we often speak of ‘the point (2, −4).’ We can think of (2, −4) as instructions
on how to reach P from the origin by moving 2 units to the right and 4 units downwards. Notice
that the order in the ordered pair is important − if we wish to plot the point (−4, 2), we would
move to the left 4 units from the origin and then move upwards 2 units, as below on the right.
y y 4 4 3 3 (−4, 2)
2
1 −4 −3 −2 2
1 −1 1 2 3 4 x −4 −3 −2 −1 1 −1
−2 3 4 x −2 −3 2 −1 −3 −4 P −4 P (2,...
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 Fall '13
 Wong
 Algebra, Trigonometry, Cartesian Coordinate System, The Land, The Waves, René Descartes, Euclidean geometry

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