For what value of λ are the vector 
and 
perpendicular to each other? Where :
and 
Now
λ × 4 + 2 × (-9) + 1 × 2 = 0
λ × 4 = 16
λ = 4
2
For what value of λ are the vector and perpendicular to each other? Where :
and
Now
λ × 4 + 2 × (-9) + 1 × 2 = 0
λ × 4 = 16
λ = 4