Lesson 1ª

WHAT ARE COORDINATES?

Cartesian coordinates are lines used to locate the position of a point in a map, a plane, etc. They are called Cartesian coordinates because of their inventor René Descartes (1640's).

Let's get to work. In a clean sheet of paper (a sheet of paper is actually a plane), draw a vertical line using a ruler. Then, draw a horizontal line cutting the vertical line in the middle. See the image below:

Now, we will divide both lines into equal parts. The place where they intersect is called the origin (or sometimes zero). Mark this point with a red dot. This is (0,0).

Positive numbers are placed to the right of the origin and from the origin up; negative numbers are placed to the left of the origin and going down from it.

For example, when it is very cold, we mention temperatures below zero or negative temperatures. These would go below the origin and temperatures above zero would go above the origin.

Now, measure and write small divisions on each line. Number them starting from the origin (zero - 0). We will make 4 markings on each line: two positive markings to the right of the horizontal line and two negative markings to the left. Two positive markings above the origin on the vertical line and two negative markings below the origin. The example below shows more numbers:

The horizontal line is called the X-axis. However, it is also called the abscissa axis. This comes from the latin abscissa, which means a line which is cut.

The vertical line is called the Y-axis. It is also called the ordinate axis. This word is said to come from the latin word ordiñatae. Others think it comes from the greek word orthia, which means straight and upward.

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