The angle between the lines whose direction cosines satisfy the equations l + m + n = 0 and l^{2} + m^{2} + n^{2} = 0 is

- π/2
- π/3
- π/4
- π/6

**Answer**

l = -m -n

m^{2} + n^{2} = (m + n)^{2}

mn = 0

So possibilities are (-1/√2,1/√2,0) and (1/√2,0,1/√2)

**The correct option is B.**