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.


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.