Idiot\'s Guides Basic Math and Pre-Algebra

134 Part 2: Into the Unknown

The Coordinate Plane ...........................................................................................................

Take a sheet of paper and draw a horizontal number line across the middle of the sheet. Then

draw a vertical number line, so that the two lines have their zero in the same spot. With just

those two lines in place, you can direct someone to any point on the paper by giving them a

number on the horizontal line and one on the vertical line. It’s as if those two numbers were the

names of streets, 4th Street and 5th Avenue, and you wanted to meet someone on the corner.

The horizontal number line is called the x-axis, and the vertical one is called the y-axis. Every

point is represented by a pair of numbers, (x,y). The point in our example is the point (4,5).

The two numbers are called the coordinates of the point. 4 is the x-coordinate, and 5 is the

y-coordinate. To locate the point, start at the spot that is 0 on both number lines. This point (0,0)

is called the origin. Count left or right according to the first coordinate. In this case, count 4 to

the right. Then let the y-coordinate tell you how far up or down to go. In this case, go up 5.

-6 -2 062

-2

2

4

6

-4

-6

-8-9 -7 -5 -4 -1-3 134 5 78 9

-8

-9

-1

-3

-5

-7

8

9

1

3

5

7

-10 10

-10

10

y

x