The Cartesian Coordinate System The Cartesian Coordinate system is two dimensional grid formed by drawing two numbers lines; one line is perpendicular to the other. The horizontal number line is called the X axis. The vertical number line is called the Y axis. The point at which the two axes intersect is called the ORIGIN.

The Cartesian Coordinate System Quadrant I is in the upper right corner . The axes divide the grid into four quadrants. The other three are labeled counterclockwise from I. Label the other three quadrants.

The Cartesian Coordinate System Let’s label the scale on this coordinate system. On the x axis, label each mark to the right of the origin with positive integers; label each mark to the left of origin with negative integers, starting with –1 and decreasing as you go left. On the y axis, label each mark above the origin with positive integers; label each mark below the origin with negative integers, starting with –1 and decreasing as you go down.

( a, b ) Ordered Pair Notation We can locate points on the coordinate system using ordered pairs of numbers. ( a, b ) The first number is called the “x coordinate”. The absolute value of this number tells us how many spaces to count horizontally. We count right if the x-coordinate is positive. We count left if the x-coordinate is negative. The second number is called the “y coordinate”. The absolute value of this number tells us how many spaces to count vertically. We count up if the y-coordinate is positive. We count down if the y-coordinate is negative.