One method to develop a plan for a proof is to work “backwards” by starting with the conclusion
2 answers:
You might be interested in
The cross product of two vectors gives a third vector 
that is orthogonal to the first two.
Normalize this vector by dividing it by its norm:
To get another vector orthogonal to the first two, you can just change the sign and use
.
Normalize this vector by dividing it by its norm:
To get another vector orthogonal to the first two, you can just change the sign and use