Manipal Entrance Test 2016 Math Paper

Given, 1+m+n=0...(i)
and lm=0
Either m=0 or l=0
If l=0, then put in Eq. (i), we get
m=−n
∴ Direction ratios are 0,−n,n i.e. 0,-1, 1
If m=0, then put in Eq (i), we get l=−n
∴ Direction ratios are −n,0,n i.e. -1, 0, 1. ⇒θ=

π

3