Answer
(a) $0$
(b) Yes.
Work Step by Step
(a) Given $\vec u=2i-j+4k$ and $\vec u=3i+2j-k$, by definition the dot product is given by $\vec u\cdot\vec v=2\times3-1\times2+4\times(-1)=0$
(b) Since $\vec u\cdot\vec v=0$, the two vectors are perpendicular to each other.
