The correct option is D π/3
We have
l+m−n=0
and l2+m2+n2=0
⇒l2+m2=n2 and l+m=n
⇒l2+m2=(l+m)2
⇒2lm=0
⇒l=0,m=0
If l=0, then m=n
∴l0=m1=n1
If m=0, then
l=n
∴l1=m0=n1
thus, the dr's of the lines are proportional to 0,1,1 and 1,0,1
Therefore, angle θ between them is given by
cosθ=0×1+1×0+|1×1|√0+1+1√1+0+1=12
⇒θ=π3