Direction Cosine

If l,m,n are direction cosines of the line then -l,-m,-n can be: a) only direction ratios of the line b) only direction cosines of the line c) direction cosines and direction ratios of the line d) neither direction cosines nor direction ratios of the line

If the directions cosines of a line are k, k and k then ..........

If the two directional cosines of a vectors are 1/sqrt(2) and 1/sqrt(3) then the value of third directional cosine is

If the two directional cosines of a vectors are 1/sqrt(2) and 1/sqrt(3) then the value of third directional cosine is