If , the do you think that A is necessarily equal to C?
Here,
Let the angle between be and that between be .
∴
and
Therefore,
Now,
and then
Thus, A is not necessarily equal to C.
What is the angle between
Vector is perpendicular to the plane containing
is the resultant of
therefore lies in the plane containing
∴ Angle between and is
Alternatively:
The unit vector perpendicular to vectors is given by,
We have,
and
Therefore,
and
∴ , is the required unit vector.