Two
vectors u,v in a
Euclidean vector space V are
orthogonal iff I(u,v)=0, where I is the
inner product associated with V.
In
R^n, using the
standard inner product or "dot product", (a1, a2,...,an) and (b1,b2,...,bn) are orthoganal if a1*b1+a2*b2+...+an*bn=0.