Question

Two vectors A=3i+aj+3k and B=3i-j-k are perpendicular to each other. Calculate the value of constant a

Answer 1

If they are perpendicular then dot product should be 0 so A.B=0
AxBx +AyBy +AzBz =0
Ans =6

Answer 2

They are perpendicular means their dot product is zero.
A•B = 0 = 9-a-3
< a=6 >