Show that the points `(1,-1),(5,2)` and `(9 ,5)` are collinear.

Explanation

Let `A(1,-1), B(5,2)` and `C(9,5)` be the given points. Then,we have

`AB=sqrt((5−1)^2+(2+1)^2
)=16+9
​=5`

BC=`sqrt((5−9)^2+(2−5)^2)
​=16+9
​=5`

and, AC=`sqrt((1−9)^2+(−1−5)^2)
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