Q12 of 23 Page 330

The co-ordinates of mid-points of the sides of a triangle ABC are (0, 1), (1, 1) and (1, 0); let us find the co-ordinates of its centroid.

Let the vertices of ΔABC be


A = (x1, y1) and


B = (x2, y2) and


C = (x3, y3)


Centroid of a triangle is given by


G =


Let (0, 1), (1, 1) and (1, 0) be midpoints of AB, BC and AC respectively


Point (0, 1) is the midpoint of AB


(0, 1) =


Equating x and y coordinates


= 0 and = 1


x1 + x2 = 0 … (a) and y1 + y2 = 2 … (i)


Point (1, 1) is the midpoint of BC


(1, 1) =


Equating x and y coordinates


= 1 and = 1


x2 + x3 = 2 … (b) and y2 + y3 = 2 … (ii)


Point (1, 0) is the midpoint of AC


(1, 0) =


Equating x and y coordinates


= 1 and = 0


x1 + x3 = 2 … (c) and y1 + y3 = 0 … (iii)


Adding equations (a), (b) and (c) & adding equations (i), (ii) and (iii) we get


x1 + x2 + x2 + x3 + x1 + x3 = 4 and y1 + y2 + y2 + y3 + y1 + y3 = 4


2 (x1 + x2 + x3) = 4 and 2 (y1 + y2 + y3) = 4


x1 + x2 + x3 = 2 and y1 + y2 + y3 = 2


Divide by 3


= and =


Hence centroid is G =


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