Coordinate Geometry Class 9th Notes - Free NCERT Class 9th Maths Chapter 3 Notes - Download PDF

Class 9 Coordinate Geometry Notes PDF – Download Free Study Material

Careers360 brings you NCERT Class 9 Maths Chapter 3 Coordinate Geometry notes, carefully prepared by subject experts to simplify your studies and help in exams. A downloadable PDF is available — click the link below to access it.

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NCERT Class 9 Maths Chapter 3 Coordinate Geometry Notes

Coordinate Geometry: It is an analytical geometry that is used for defining the exact position of a point using coordinates.

Cartesian System

The Cartesian system is a method of defining the position of a point in a plane. In this method, points are located using two perpendicular lines. In the Cartesian system, the horizontal line is called the X-axis and it is represented by XX', and the vertical line is called the Y-axis and it is represented by YY'.

Origin

The place where the two perpendicular lines of the X-axis and the Y-axis intersect is called the origin, and it is denoted by the letter $O$. This origin divides the line into positive and negative directions as OX and OY are called the positive direction, and OX' and OY' are called the negative direction of the graph.

Coordinate Axes and Quadrants

The origin divides the plane into four sections, and these sections are known as quadrants. Quadrants are numbered as I, II, III and IV in an anticlockwise direction starting from the top right section. The plane where these quadrants exist is called the Cartesian plane, coordinate plane or XY plane and the axes on this Cartesian plane are called coordinate axes.

Points in Different Quadrants

The four quadrants in the XY plane are as follows,
Quadrant I: It is represented by (+, +) signs, which means X and Y are both positive.
Example: (2, 7)
Quadrant II: It is represented by (–, +) signs, which means X is negative and Y is positive.
Example: (-3, 4)
Quadrant III: It is represented by (–, –) signs, which means X and Y are both negative.
Example: (-4,-4)
Quadrant IV: It is represented by (+, –) signs, which means X is positive and Y is negative.
Example: (1, -9)

Plotting on a Graph

On the plane, a set of numbers or coordinates is given to define the position of the point in the XY plane, and these coordinate points are represented by an ordered pair of (x, y) where, X or distance from origin to X axis is called abscissa or X-coordinate and the distance from O to Y axis is called the ordinate or Y-coordinate as shown in figure.

Plotting a Point in the Plane if Its Coordinates Are Given

In the coordinate plan, the X-coordinate implies that the distance from the origin to the X-axis and the Y-coordinate implies that the distance from the origin to the Y-axis. These points can be:
Example: Plot the coordinates (1, 2), (2, -4), (-3, 4) and (-2, -2) in the Cartesian plane.
Here,
(1, 2)→It is 1 unit away from the positive y-axis and 2 units away from the positive x-axis.
(2, -4)→It is 2 units away from the positive y-axis and 4 units away from the negative x-axis.
(-3, 4)→It is 3 units away from the negative y-axis and 4 units away from the positive x-axis.
(-2, -2)→It is 2 units away from the negative y-axis and 2 units away from the negative x-axis.
The plotting of these coordinates is shown in the figure:

Coordinate Geometry: Previous Year Question and Answer

Given below are selected previous year question answers for NCERT Class 9 Maths Chapter 3 Coordinate Geometry, collected from various examinations.

Question 1:
Find the coordinates of the points where the graph $57x – 19y = 399$ cuts the coordinate axes.

Solution:
$57x-19y=399$
⇒ $\frac{57x}{399}-\frac{19y}{399} = 1$
⇒ $\frac{x}{7}-\frac{y}{21} = 1$ -------------(i)
Comparing it with the equation of a line:
$\frac{x}{a}+\frac{y}{b} = 1$
x-intercept = $a$ = 7
y-intercept = $b$ = –21
The line, $57x-19y=399$, cuts the x-axis at (7, 0) and the y-axis at (0, –21)
Hence, the correct answer is 'x-axis at (7, 0) and y-axis at (0, –21)'.

Question 2:
The graph of the equation $x=a(a \neq 0)$ is a_____.

Solution:
Given: $x=a(a \neq 0)$
A diagram that shows the change of one variable to one or more other variables, such as a collection of one or more points, lines, line segments, curves, or regions.
The value of $x$ = The value of $a$ = 1, 2, 3, and so on to infinity.
The value of $y$ = constant (assume $y=4$)
As a result, the graph these points create will be a straight line parallel to the y-axis.
Hence, the correct answer is a line parallel to the y-axis.

Question 3:
At what point does the line $3x+y=-6$ intercept the x-axis?

Solution:
At an x-intercept, y = 0.
So, 3x + 0 = – 6
Solving for x,
⇒ 3x = – 6
⇒ x = – 2
So, the required intercept point = (–2, 0)
Hence, the correct answer is (–2, 0).

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