Chapter 1
Orienting Yourself: The Use of Coordinates
CBSE Class 9
Mathematics Solutions
Educart Mathematics class Class 9 NCERT Exemplar cover
Question:

Are the points M (-3, -4), A (0, 0) and G (6, 8) on the same straight line? Suggest a method to check this without plotting and joining the points.

Answer: Verified

Given, points M(3,4)M(-3, -4), A(0,0)A(0, 0) and G(6,8)G(6, 8).
To check collinearity, we use the distance formula and verify:

MA+AG=MGMA + AG = MG

By distance formula, we have

D=(x2x1)2+(y2y1)2D = \sqrt{(x_2 - x_1)^2 + (y_2 - y_1)^2}

MA=[0(3)]2+[0(4)]2MA = \sqrt{[0 - (-3)]^2 + [0 - (-4)]^2}

=(32+42)=9+16= \sqrt{(3^2 + 4^2)} = \sqrt{9 + 16}

=25=5= \sqrt{25} = 5

AG=(60)2+(80)2AG = \sqrt{(6 - 0)^2 + (8 - 0)^2}

=36+64=100=10= \sqrt{36 + 64} = \sqrt{100} = 10

MG=[6(3)]2+[8(4)]2MG = \sqrt{[6 - (-3)]^2 + [8 - (-4)]^2}

=92+122=81+144= \sqrt{9^2 + 12^2} = \sqrt{81 + 144}

=225=15= \sqrt{225} = 15

Now, MA+AG=5+10=15=MG\text{Now, } MA + AG = 5 + 10 = 15 = MG

Hence, the given three points are collinear.

## Concept Applied

Three points are collinear when the sum of the two shorter distances between them is exactly equal to the longest distance.

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