Answer
(a) not meaningful.
(b) meaningful.
(c) meaningful.
(d) meaningful.
Work Step by Step
(a) not meaningful since $ u\cdot v $ is a scalar and a scalar dot product with a vector is not defined.
(b) meaningful since $ u\times v $ is a vector and a vector dot product with a vector is defined.
(c) meaningful since $\|w\|$ and $ u\cdot v $ are scalars and the product of scalars is defined.
(d) meaningful since $\|w\|$ is a scalar and $ u\times v $ are scalars and a scalar times a vector is defined.
