Practice!

Sample Problem

Are (-1, 1), (2, 2), and (6, 5) collinear?

Solution

Three points (x1, y1), (x2, y2), and (x3, y3) are collinear (lie on the same line) if and only if

Therefore, with the points (-1, 1), (2, 2), and (6, 5) – we have (expanding on the first row)

Because the value of this determinant is not zero, the three points do not lie on the same line (not collinear).