Question

prove that the vectors a vector =i vector +2j vector + 3k vector and b vector =2i vector-j vector are perpendicular to each other.

Answer 1

see attachment...........hope it helps

Answer 2

two vectors are perpendicular means
dot product of its are equal to zero .

given,

A = i + 2j + 3k

B = 2i -j + 0k

now, A.B = (1) (2) +(2)(-1) +(3)(0)
=0
here we see that dot of A and B equal to zero , so A and B must be perpendicular to each other