## Co-ordinate axes

X'OX and Y'OY are known as co-ordinate axes. The horizontal line X'OX is called the x-axis. The vertical line Y'OY is called the y-axis. The point O is called the origin.

The co-ordinate axis divide the graph into four regions. each region is called a quadrant.
The region XOY is called the First Quadrant.
The region Y'OX' is called the Second Quadrant.
The region X'OY' is called the Third Quadrant.
The region Y'OX is called the Fourth Quadrant.

## Ordered Pair

A pair listed like (a,b) is called an ordered pair if the positions of a and b cannot be changed.

## Co-ordinates of a point

1. Distance of P,Q,R and S from the Y axis in number of units is called the x-co-ordinate or abscissa of P, Q, R and S.
2. Distance of P,Q,R and S from the X axis in number of units is called the y-co-ordinate or ordinate of P, Q, R and S.
We write both the co-ordinates in ordered pair (x,y). Where x is the abscissa and y is the ordinate. The distance on x axis is taken positive to right of y-axis and negative to left of y-axis. The distance on y-axis is taken positive to the above of x-axis and negative to the below of x-axis.

The four points P, Q, R and S has coordinates (3,7),(-5,8),(-4,-2) and (10,8) respectively.

Any point on x-axis has co-ordinate  (x,0).
Any point on y-axis has co-ordinate  (0,y).