### Coordinate Geometry - Revision Notes

CBSE Class 09 Mathematics

Revision Notes

CHAPTER – 3

COORDINATE GEOMETRY

1. Cartesian System

2. Plotting a Point in the Plane with given Coordinates

Coordinate Geometry : The branch of mathematics in which geometric problems are solved through algebra by using the coordinate system is known as coordinate geometry.

Coordinate System

Coordinate axes: The position of a point in a plane is determined with reference to two fixed mutually perpendicular lines, called the coordinate axes.

In this system, position of a point is described by ordered pair of two numbers.

Quadrants: The coordinate axes divide the plane into four parts which are known as quadrants.

Ordered pair : A pair of numbers a and b listed in a specific order with 'a' at the first place and 'b' at the second place is called an ordered pair (a,b)

Note that

Thus (2,3) is one ordered pair and (3,2) is another ordered pair.

In given figure O is called origin.

The horizontal line

XOX' is called the -axis.

The vertical line YOY' is called the -axis.

P(a,b) be any point in the plane. 'a' the first number denotes the distance of point from

-axis and 'b' the second number denotes the distance of point from -axis.

a - X - coordinate | abscissa of P.

b - Y - coordinate | ordinate of P.

The point of intersection of the coordinate axes is called the origin.

The coordinates of origin are (0,0)

Every point on the x-axis is at a distance o unit from the -axis. So its ordinate is 0.

Every point on the y-axis is at a distance of unit from the -axis. So, its abscissa is 0.

Note : Any point lying on - axis or - axis does not lie in any quadrant.

The sign of coordinates (x, y) of a point in various quadrant are as given below:

Quadrant | Coordinates | |

x | y | |

I | + | + |

II | - | + |

III | - | - |

IV | + | - |