## Orthogonality relation

W.r.t. the standard scalar product decide which pairs of the following three vectors are orthogonal: $$(1, 2, 3)$$, $$(5, 2, -3)$$ and $$(-2, -1, -4)$$.
$$(1, 2, 3)\perp(5, 2, -3)$$, $$(5, 2, -3)\perp(-2, -1, -4)$$, but $$(1, 2, 3)\not\perp(-2, -1, -4)$$.