## Cartesian Coordinate Plane

We draw graphs on a coordinate plane. It is called the Cartesian Coordinate Plane, named after Rene Decartes, who developed these processes. Let’s get to the basics here.

**Definitions**

**Coordinate Plane**: A two-dimension surface. The dimensions are up/down, which we call *y*, and left/right, which we call* x*.

**Axis:** We have two axes (plural of axis).

- The horizontal axis is the
*x*– axis. - The
*x*– axis is a number line, zero at the center.- To the left is negative, to the right is positive.

- The vertical axis is the
*y*– axis. - The
*y –*axis is a number line, zero at the center.- Down is negative, up is positive.

- The two axes intersect where
*x*= 0 and*y*= 0. This is a coordinate of (0, 0), called the origin. - The axes divide the plane into four quadrants. Top right is one, top left is two, bottom left is three and bottom right is four.

**Coordinate**: A location. In this application, the location is written as an ordered pair. Think of a coordinate as an address, the *x* number is first, which goes left to right. The *y* number is second, which goes up and down.

**Ordered Pair**: A pair of numbers, *x* and *y*, written in parenthesis (*x, y*). *x* is the input to an equation and *y* is the output of the equation.

**Plotting a Point:** To plot a point you start at the origin. You count the distance noted in the *x* – coordinate of the order pair, then count the distance noted in the *y* – coordinate of the order pair.