Plotting on the Coordinate Plane Lesson 4.02

After completing this lesson, you will be able to say: I can identify and position pairs of rational numbers on a coordinate plane.

Plotting Points In order to understand how to plot points on a coordinate plane, we must first recall how to locate integers on horizontal and vertical number line diagrams Point R is on –7. The negative shows that the point is 7 spaces to the left of 0. Point T is on 9. This is positive, so the point is 9 spaces to the right of 0.

Plotting Points Let’s plot point S at 4 and point P at –5 on a vertical number line. Point P is on –5. The negative shows that the point is 5 spaces below 0. Point S is on 4. This is positive, so the point is 4 spaces above 0.

Plotting a Point Plot the point (3,1) Start at the origin. (Remember the first number tells you how far to go left or right.) Because the first coordinate is positive three, you should travel three units to the right. The second number tells you up or down. The second number is positive so you will move up 1 unit Place a dot here to mark your point.

Example Richard’s ticket says that he is sitting at (–3, 4). Let’s find his location!

Try It! Jen’s ticket says she is seated at (0, –2). Plot the point to help Jen find her seat!

Check your work

Rational Numbers Rational numbers can be integers, decimals, or fractions. Plotting decimals and fractions on a number line is as easy as plotting any integer; you just have to think about the values in between integers. Let’s Plot the point (3.5, 0.5) Plotting decimals is similar to plotting integers. Follow the same steps: 1. Start at the origin. 2. Move 3.5 units to the right. The 3.5 is in the middle of 3 and Then go up 0.5. The 0.5 is in the middle of 0 and Plot the point.

Example Doris wants to buy some cupcakes. The cupcake stand is located at (−5, 2 3/4). Let’s help Doris figure out where it is by plotting the cupcake stand on the coordinate plane!

Try It

Check your work

Determining the Coordinates of a Point We need to find the coordinates of Point P It is in the second quadrant. So we already know that the x-coordinate will be negative and the y- coordinate will be positive. The first number of the ordered pair is the x- coordinate. Count along the x-axis to find how many units left of the origin the point lies. This point is three units left of the origin. So the first number in the ordered pair is −3. The second number in the ordered pair is the y-coordinate. You must find out how many units the point is above the x-axis. Because Point P is 2 units above the x-axis, the y-coordinate is 2. That means the coordinates of Point P are (−3, 2)

Try It Plot the points on the coordinate plane A (2, 4) B (-1/2, -3) C (2.75, -4)

Check your work A (2, 4) B (-1/2, -3) C (2.75, -4) A B C

Now that you completed this lesson, you should be able to say: I can identify and position pairs of rational numbers on a coordinate plane.