3.1: The Cartesian Plane
Kaitlyn walked into Math class and saw the following image displayed from the overhead projector. Her teacher asked everyone in the class to duplicate the picture on the blank sheet of paper that she had placed on each student’s desk.
When the teacher felt that the students had completed the drawing, she asked them to share their results with the class. Most of the students had difficulty reproducing the picture. Kaitlyn told the class that she could not make the picture the same size as the one shown. She also said that she had a problem locating the leaves in the same places on the stem. Her teacher said that she could offer a solution to these problems.
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Khan Academy The Coordinate Plane
Guidance
The Cartesian plane is a system of four areas or quadrants produced by the perpendicular intersection of two number lines. The two number lines intersect at right angles. The point of intersection is known as the origin. One number line is a horizontal line and this is called the
The value of the origin on the
Every point that is plotted on a Cartesian plane has two values associated with it. The first value represents the
To plot a point on the Cartesian plane:
 Start at zero (the origin) and locate the
x− coordinate on thex axis.  If the
x− coordinate is positive, move to the right of the origin the number of units displayed by the number. If thex− coordinate is negative, move to the left of the origin the number of units displayed by the number.  Once the
x− coordinate (also called the abscissa) has been located, move vertically the number of units displayed by they− coordinate (also called the ordinate). If they− coordinate is positive, move vertically upward from thex− coordinate, the number of units displayed by they− coordinate. If they− coordinate is negative, move vertically downward from thex− coordinate, the number of units displayed by they− coordinate.  The point is can now be plotted.
Examine the points

A(−4,2) – From the origin, move to the left four units (along the red line on thex axis). Now, move vertically upward two units. Plot the pointA . 
B(−2,−1) – From the origin, move to the left two units (along the red line on thex axis). Now, move vertically downward one unit. Plot the pointB . 
C(3,−4) – From the origin, move to the right three units (along the red line on thex axis). Now, move vertically downward four units. Plot the pointC . 
D(6,3) – From the origin, move to the right six units (along the red line on thex axis). Now, move vertically upward three units. Plot the pointD .
Example A
For each quadrant, say whether the values of
Solution: The graph below shows where
Example B
On the following Cartesian plane, draw an
Solution:
Example C
Determine the coordinates of each of the plotted points on the following graph.
Solution:
Concept Problem Revisited
Now, let us return to the beginning of the lesson to find out the solution that the teacher had for the students.
Now that the students can see the picture on a Cartesian plane, the reproduction process should be much easier.
Vocabulary
 Abscissa

The abscissa is the
x− coordinate of the ordered pair that represents a plotted point on a Cartesian plane. For the point (3, 7), 3 is the abscissa.
 Cartesian Plane
 A Cartesian plane is a system of four areas or quadrants produced by the perpendicular intersection of two number lines. A Cartesian plane is the grid on which points are plotted.
 Coordinates

The coordinates are the ordered pair
(x,y) that represent a point on the Cartesian plane.
 Coordinate Plane
 The coordinate plane is another name for the Cartesian plane.
 Ordinate

The ordinate is the
y coordinate of the ordered pair that represents a plotted point on a Cartesian plane. For the point (3, 7), 7 is the ordinate
 Origin

The origin is the point of intersection of the
x andy axes on the Cartesian plane. The coordinates of the origin are (0, 0).

x axis 
The
x axis is the horizontal number line of the Cartesian plane.

y axis 
The
y axis is the vertical number line of the Cartesian plane.
Guided Practice
1. Draw a Cartesian plane that displays only positive values. Number the
 LINE 1 (6, 0) (8, 0) (9, 1) (10, 3) (10, 6) (9, 8) (7, 9) (5, 9) STOP
 LINE 2 (6, 0) (4, 0) (3, 1) (2, 3) (2, 6) (3, 8) (5, 9) STOP
 LINE 3 (7, 9) (6, 12) (4, 11) (5, 9) STOP
 LINE 4 (4, 8) (3, 6) (5, 6) (4, 8) STOP
 LINE 5 (8, 8) (7, 6) (9, 6) (8, 8) STOP
 LINE 6 (5, 5) (7, 5) (6, 3) (5, 5) STOP
 LINE 7 (3, 2) (4, 1) (5, 2) (6, 1) (7, 2) (8, 1) (9, 2) STOP
 LINE 8 (4, 1) (6, 1) (8, 1) STOP
2. In which quadrant would the following points be located?
 i) (3, 8)
 ii) (5, 4)
 iii) (7, 2)
 iv) (6, 9)
 v) (3, 3)
 vi) (9, 7)
3. State the coordinates of the points plotted on the following Cartesian plane.
Answers:
1. The following picture is the result of plotting the coordinates and joining them in the order in which they were plotted. Your pumpkin can be any color you like.
2. i) (3, 8) – the

ii) (5, 4) – the
x coordinate is negative and they− coordinate is positive. This point will be located in Quadrant II. 
iii) (7, 2) – the
x coordinate is positive and they− coordinate is positive. This point will be located in Quadrant I. 
iv) (6, 9) – the
x coordinate is negative and they− coordinate is negative. This point will be located in Quadrant III. 
v) (3, 3) – the
x coordinate is negative and they− coordinate is positive. This point will be located in Quadrant II. 
vi) (9, 7) – the
x coordinate is positive and they− coordinate is negative. This point will be located in Quadrant IV.
3.
Practice
Answer the following questions with respect to the Cartesian plane:
 What name is given to the horizontal number line on the Cartesian plane?
 What name is given to the four areas of the Cartesian plane?
 What are the coordinates of the origin?
 What name is given to the vertical number line on the Cartesian plane?
 What other name is often used to refer to the
x− coordinate of a point on the Cartesian plane?
On each of the following graphs, select three points and state the coordinates of these points.
 With a partner, create a picture on a Cartesian plane that is numbered ten round. Using the coordinates, list the points for at least five lines necessary for a classmate to complete this same picture. (Go back to the directions for the pumpkin).
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Image Attributions
Here you will learn about the Cartesian plane and review how to plot points on the Cartesian plane.
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