Coordinate Geometry Class 9 Notes Maths - Chapter 4

Chapter: 4

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The system used for describing the position of a point in a plane is known as cartesian system.
In this system, a plane is divided into four parts (called quadrants) with the help of two perpendicular lines.

The two perpendicular lines, which divides the plane, are called the coordinate axes.
The horizontal line (XX’) is called the x-axis and the vertical line (YY’) is called the y-axis.
The point of intersection of these lines is called origin and it is denoted by O.

If a is abscissa and b is ordinate of a point then (a, b) are called the coordinates of the point.
In (a, b) a is also called the x – coordinate and b is also called the y – coordinate.
Here, the x – coordinate comes first and y – coordinate comes second. Therefore, (a, b) is an odered pair. If (a, b) ≠ (b, a) then, a ≠ b and if (a, b) = (b, a), then a = b.
Coordinates of a point on the x – axis are of the form (a, 0) and that of the point on the y-axis are of the form (O, b).
Coordinates of the origin are (0,0).
Signs of the coordinates of a point in the first quadrant are (+ , +) in the second quadrant (–, +), in the third quadrant (–, –) and in the fourth quadrant (+, –).

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