AAKASH AITS( 3D )

For the abv eq^ns ..the cross product of their normals of the planes..give the direction ratios of the line passing through them..
for it to be a single line..

drs of the line passing through 3x - y - 2z = 0 and x - y + 2z = 0 is (1,4,1)

drs of the line passing through x - y + 2z = 0 and x + y -kz = 0 is (k-2, k+2, 2)
comparing the drs of the two lines K = 6
so ans is D

OR

u can use .
cramers rule

det = 0 and individual dets (D1, D2, D3)= 0

sorry if i sound ambiguous .. its just dat ive lost track of what the names of things r.