For what value of λ are the vector 
and 
perpendicular to each other? Where :
and 
Now
λ × 1 + 3 × (-1) + 2 × 3 = 0
λ - 3 + 6 = 0
λ = -3
2
For what value of λ are the vector and perpendicular to each other? Where :
and
Now
λ × 1 + 3 × (-1) + 2 × 3 = 0
λ - 3 + 6 = 0
λ = -3