Therefore a vector which has the same direction as and has the magnitude 3 has the components:
And therefore you have to solve for x:
(since only the positive value should be used). That means:
Let . Let
Then you know:
and therefore the vector
is perpendicular to
Actually this is the equation of a plane passing through the origin with as it's normal vector.
Choose numbers for r and s to build vectors and do the required examinations.