For three points to be collinear, the slope of all pairs must be equal, that is the slope of AB = slope of BC = slope of CA

Given points are A(5, 1), B(1, -1) and C(x, 4)

Slope of AB =

The slope of BC =

Slope of CA =

The slope of all lines must be the same

Note:- We can use any two points to get the value of “x”.