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Question

If the points(7,−2),(5,1),(3,K)are collinear,then the value of K is :

A
2
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B
4
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C
6
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D
8
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Solution

The correct option is C 4

Since the given points are collinear, they do not form a
triangle, which means area of the triangle is Zero.

Area
of a triangle with vertices (x1,y1) ; (x2,y2) and (x3,y3) is x1(y2y3)+x2(y3y1)+x3(y1y2)2

Hence, substituting the points (x1,y1)=(7,2) ; (x2,y2)=(5,12) and (x3,y3)=(3,k)
in the area formula, we get
7(1k)+5(k+2)+3(21)2=0
=>77k+5k+109=0
=>2k=8

=>k=4

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