 # Coordinate Geometry Class 9 Notes - Chapter 3

## Introduction to Coordinate Geometry

Coordinate geometry is the branch of geometry, where the position of the points on the plane is defined with the help of an ordered pair of numbers known as coordinates. Coordinate geometry class 9 notes are provided here to help learners understand the concept in an easy manner.

### Coordinate Axes and Cartesian Plane

Two perpendicular lines, one horizontal line and the other vertical line is required for locating a point or an object in a plane. These perpendicular lines are called the coordinate Axes and the plane is called the coordinate plane also known as the Cartesian plane.

The horizontal and vertical lines are called x-axis and y-axis respectively. These x and y coordinate axes divide the cartesian plane into 4 identical parts known as quadrants and the point of intersection of x and y-axes is called origin, generally denoted by ‘o’.

### Abscissa and Ordinate

The distance between y-axis and any point in a plane is called its x coordinate, also known as abscissa. Similarly, the distance between x-axis and any point in a plane is called its y coordinate, also known as ordinate. If x and y are the abscissa and the ordinate of a point Q, then, (x, y) are called the coordinates of point Q. The general form of coordinates of a point on the x-axis is (x, 0) and that of the point on the y-axis are (0, y).

The coordinates of the origin ‘o’ are (0, 0). If a positive real number is denoted by ‘+’ and a negative real number is denoted by ‘-‘, then, the sign convention of coordinates in 1st quadrant is (+, +), In 2nd quadrant (–, +), in 3rd quadrant (–, –), and in the fourth quadrant (+, –). Also, If x is not equal to y, then the values (x, y) will not be equal to (y, x). The coordinates (x, y) and (y, x) are equal if, x = y.

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