Question 319897
To do this, you will need to find the slope 3 times.

You need the slope from A to B, from B to C and from A to C.  If they all share the same slope, then all 3 points lie on the same line.

Slope from A to B = (1-5)/6-2) = -4/4 or -1.

Slope from B to C = (-1-1)/(8-6) = -2/2 or -1.

Slope from A to C = (-1-5)/(8-2) = -6/6 = -1.

They all share slope -1 and so they all lie on the same line.