Question:
For two vectors A and B,
$|A+B|=|A-B|$ is always true when
(a) $|A|=|B| \neq 0$
(b) $A \perp B$
(c) $|A|=|B| \neq 0$ and $\mathrm{A}$ and $\mathrm{B}$ are parallel or antiparallel
(d) $|A|$ or $|B|$ is zero
Solution:
The correct answer is (b)
$A \perp B$ and (d) when either
$|A|$ or $|B|$ is zero