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.
Watch This
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 \begin{align*}x\end{align*}
The value of the origin on the \begin{align*}x\end{align*}
Every point that is plotted on a Cartesian plane has two values associated with it. The first value represents the \begin{align*}x\end{align*}
To plot a point on the Cartesian plane:
 Start at zero (the origin) and locate the \begin{align*}x\end{align*}
x− coordinate on the \begin{align*}x\end{align*}x axis.  If the \begin{align*}x\end{align*}
x− coordinate is positive, move to the right of the origin the number of units displayed by the number. If the \begin{align*}x\end{align*}x− coordinate is negative, move to the left of the origin the number of units displayed by the number.  Once the \begin{align*}x\end{align*}
x− coordinate (also called the abscissa) has been located, move vertically the number of units displayed by the \begin{align*}y\end{align*}y− coordinate (also called the ordinate). If the \begin{align*}y\end{align*}y− coordinate is positive, move vertically upward from the \begin{align*}x\end{align*}x− coordinate, the number of units displayed by the \begin{align*}y\end{align*}y− coordinate. If the \begin{align*}y\end{align*}y− coordinate is negative, move vertically downward from the \begin{align*}x\end{align*}x− coordinate, the number of units displayed by the \begin{align*}y\end{align*}y− coordinate.  The point is can now be plotted.
Examine the points \begin{align*}A, B, C\end{align*}

\begin{align*}A (4, 2)\end{align*}
A(−4,2) – From the origin, move to the left four units (along the red line on the \begin{align*}x\end{align*}x axis). Now, move vertically upward two units. Plot the point \begin{align*}A\end{align*}A . 
\begin{align*}B (2, 1)\end{align*}
B(−2,−1) – From the origin, move to the left two units (along the red line on the \begin{align*}x\end{align*}x axis). Now, move vertically downward one unit. Plot the point \begin{align*}B\end{align*}B . 
\begin{align*}C (3, 4)\end{align*}
C(3,−4) – From the origin, move to the right three units (along the red line on the \begin{align*}x\end{align*}x axis). Now, move vertically downward four units. Plot the point \begin{align*}C\end{align*}C . 
\begin{align*}D (6, 3)\end{align*}
D(6,3) – From the origin, move to the right six units (along the red line on the \begin{align*}x\end{align*}x axis). Now, move vertically upward three units. Plot the point \begin{align*}D\end{align*}D .
Example A
For each quadrant, say whether the values of \begin{align*}x\end{align*}
Solution: The graph below shows where \begin{align*}x\end{align*}
Example B
On the following Cartesian plane, draw an \begin{align*}xy\end{align*}
\begin{align*}A(5,3) \quad B(3,2) \quad C(4,5) \quad D(4,1)\end{align*}
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 \begin{align*}x\end{align*}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 \begin{align*}(x, y)\end{align*} 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 \begin{align*}y\end{align*} 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 \begin{align*}x\end{align*} and \begin{align*}y\end{align*} axes on the Cartesian plane. The coordinates of the origin are (0, 0).
 \begin{align*}x\end{align*}axis
 The \begin{align*}x\end{align*}axis is the horizontal number line of the Cartesian plane.
 \begin{align*}y\end{align*}axis
 The \begin{align*}y\end{align*}axis is the vertical number line of the Cartesian plane.
Guided Practice
1. Draw a Cartesian plane that displays only positive values. Number the \begin{align*}x\end{align*} and \begin{align*}y\end{align*} axes to twelve. Plot the following coordinates and connect them in order. Use a straight edge to connect the points. When the word “STOP” appears, begin the next line. Plot the points in the order they appear in each Line row.
 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 \begin{align*}x\end{align*} coordinate is positive and the \begin{align*}y\end{align*}coordinate is negative. This point will be located in Quadrant IV.
 ii) (5, 4) – the \begin{align*}x\end{align*} coordinate is negative and the \begin{align*}y\end{align*}coordinate is positive. This point will be located in Quadrant II.
 iii) (7, 2) – the \begin{align*}x\end{align*} coordinate is positive and the \begin{align*}y\end{align*}coordinate is positive. This point will be located in Quadrant I.
 iv) (6, 9) – the \begin{align*}x\end{align*} coordinate is negative and the \begin{align*}y\end{align*}coordinate is negative. This point will be located in Quadrant III.
 v) (3, 3) – the \begin{align*}x\end{align*} coordinate is negative and the \begin{align*}y\end{align*}coordinate is positive. This point will be located in Quadrant II.
 vi) (9, 7) – the \begin{align*}x\end{align*} coordinate is positive and the \begin{align*}y\end{align*}coordinate is negative. This point will be located in Quadrant IV.
3. \begin{align*}A(4,4) \quad B(10,8) \quad C(8,1) \quad D(6,6) \quad E(0,5) \quad F(3,0) \quad G(2,5) \quad H(0,0)\end{align*}
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 \begin{align*}x\end{align*}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).
Image Attributions
Here you will learn about the Cartesian plane and review how to plot points on the Cartesian plane.
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