Which of the following expresses the fact that the vectors $u$ and $v$ have the same length?

Question

Which of the following expresses the fact that the vectors $u$ and $v$ have the same length?

(a) $u · u = v · v$

(b) $||u + v|| = ||u|| − ||v||$

(c) ${u \over||u||} = {v \over ||v||}$

(d) $||u + v|| = ||u|| + ||v||$

So my thoughts are, definitely not the last one or first. I think it would be b but it would be nice to get other opinions.

Answer 1

it's the first because $u\cdot u$ is the length squared.