The correct option is B 1√6,2√6,1√6
We know that the direction ratios are proportional to direction cosines i.e. l= k.a, m= k.b , n= k.c where k is any constant, l ,m & n are direction cosines and a,b & c are direction ratios.
We also know that l2+m2+n2=1
In the question given direction ratios or a,b,c are 1, 2, 1.
So the direction cosines will be -
or,l=√16(on taking k as √16)
Similarly ,m=2.√16 & n=√16
Also,-√16,−2.√16,−√16 on taking k as −√16