Coordinate Geometry Class 9 Notes Maths - Chapter 4

Chapter: 4

What Are Coordinate Geometry ?

Cartesian System

  • 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.

Coordinate Axes And Origin

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

Abscissa And Ordinate

  • Abscissa of a point is its distance from the y-axis.
  • Ordinate of a point is its distance from the x-axis.

Coordinates Of A Point

  • 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 โ€“ coordinate and b is also called the y โ€“ coordinate.
  • Here, the x โ€“ coordinate comes first and y โ€“ coordinate comes second. Therefore, (a, b) is an odered pair. If (a, b) โ‰  (b, a) then, a โ‰  b and if (a, b) = (b, a), then a = b.
  • Coordinates of a point on the x โ€“ 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 (โ€“, +), in the third quadrant (โ€“, โ€“) and in the fourth quadrant (+, โ€“).