Question

Find the value of x for which the points (x,-1), (2,1) and (4,5) are collinear.
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Answer 1

Let the points be A(x,-1), B(2,1), C(4,5)
If these three points are collinear
Then
Slope of line AB = slope of line BC
$Slope=\frac{y_2-y_1}{x_2-x_1}$
$\frac{1+1}{2-x}=\frac{5-1}{4-2}$
$\frac{2}{2-x}=\frac{4}{2}$
$\frac{2}{2-x}=2$
2-x=1
x=1
value of x=1