Question

Which of the following group is not direction cosines of a line : 

(a) 1,1,1 

(b) 0,0, -1 

(c) -1,0,0 

(d) 0,-1,0

Answer 1

Answer is (a)

Direction cosines of a line are proportional to direction ratio’s. 

Let a, b and c are direction ratio’s, then according to question