Coordinate Geometry Notes: Class 9 Maths Chapter 3
Class 9 Maths Chapter 3 Coordinate Geometry covers the Cartesian coordinate system, the x-axis and y-axis, quadrants, and how to plot points in the plane.
Overview of Topics & Subtopics (Click to Jump)
1. Cartesian System
Short Note:
• The plane formed by two perpendicular number lines, one horizontal (x-axis) and one vertical (y-axis), is called the Cartesian plane.
• The point of intersection of the axes is called the origin, denoted O, with coordinates (0, 0).
• The axes divide the plane into four quadrants: I (+, +), II (−, +), III (−, −), IV (+, −).
2. Coordinates of a Point
Short Note:
• Every point in the plane has an ordered pair of coordinates (x, y): x is the abscissa (distance from y-axis), y is the ordinate (distance from x-axis).
• The coordinates of the origin are (0, 0). Any point on the x-axis has y = 0; any point on the y-axis has x = 0.
3. Plotting a Point in the Plane
Short Note:
• To plot a point (x, y), move x units along the x-axis (right if positive, left if negative), then y units parallel to the y-axis (up if positive, down if negative).
NCERT Textbook Exercise Questions
(3, −1) lies in Quadrant IV (x positive, y negative).
(−1, 0) lies on the negative x-axis.
(1, 2) lies in Quadrant I (x positive, y positive).