CBSE 9th Maths

Cartesian Plane: A cartesian plane is defined by two perpendicular number lines, A horizontal line$(x-axis)$  and a vertical line $(y-axis)$.

Quadrants

The cartesian plane is divided into four equal parts, called quadrants. These are named in the order as I,II,III and IV starting with the upper right and going around in anticlockwise direction.

Points in different Quadrants.

Signs of coordinates of points in different quadrants:

I Quadrant: ‘+’ x – coordinate and ‘+’ y – coordinate.

II Quadrant: ‘-’ x – coordinate and ‘+’ y – coordinate.

III Quadrant: ‘-’ x – coordinate and ‘-’ y – coordinate.

IV Quadrant: ‘+’ x – coordinate and ‘-’ y – coordinate.

The coordinates of origin O are (0, 0) because it has zero distance from both the axes, so its abscissa and ordinate both are zero.

The coordinates of a point are written by using the following conventions
(i) The x-coordinate of a point is its perpendicular distance from the Y-axis measured along the X-axis (positive along the positive direction of the X-axis and negative along the negative direction of the X-axis). The x-coordinate is also called the abscissa.

(ii) The Y-coordinates of a point is its perpendicular distance from the X-axis measured along the Y-axis (positive along the positive direction of the Y-axis and negative along the negative direction of the Y-axis). The Y-coordinate is also called the ordinate.
(iii) In stating the coordinates of a point in the coordinate plane, the x-coordinate comes first and then the Y-coordinate. We place the coordinates in brackets.