Let be a nonzero vector and a vector valued function with for all , and such that the angle between and is constant. Prove that and are orthogonal.

*Proof.* Since we have for some constant . Since the angle between and is constant we have

for some constant . Therefore, is constant. Hence, is constant, say . So, we have

Is F’(t)•B=1?

Yep, this is correct.