Using section formula, show that the points A (2, –3, 4), B (–1, 2, 1) and are collinear.
The given points are A (2, –3, 4), B (–1, 2, 1), and.
Let P be a point that divides AB in the ratio k:1.
Hence, by section formula, the coordinates of P are given by
Now, we find the value of k at which point P coincides with point C.
By taking, we obtain k = 2.
For k = 2, the coordinates of point P are.
i.e., is a point that divides AB externally in the ratio 2:1 and is the same as point P.
Hence, points A, B, and C are collinear.