Just remember that u⊥v ⇔
u·v = 0 .
Example: Given u = (1, 3, 4), I can easily
think of vectors that are perpendicular. I simply set v₃ = 0, then
think: What should I set v₁ and v₂ to be, in order that
u₁v₁ + u₂v₂ + u₃v₃ = 0?
Simple, just pick v₁ = -3 and v₂ = 1. So v =
(-3, 1, 0) is ⊥ to u.
We can similarly and easily also show that the following two
vectors are also ⊥ to u:
w = (-4, 0, 1), t = (0, -4,
3).
Please see my free H2 Mathematics Textbook for
more.