If the points (5,4,2),(8,k,−7) and (6,2,−1) are collinear, then k=

The direction ratios of the line joining the first two points and the direction ratios of the line joining the last two points are as below3,k-4,-9 and -2,2-k,6If the above lines are coincident, then the above ratios are in proportion -32=k-42-k=-32 2k-8=-6+3k k=-2