设η1,η2,...,ηs是两两正交的非零向量.k1,k2,...,ks是组合系数,使得k1·η1+k2·η2+...+ks·ηs = 0.对i = 1,2,...,s,两边与ηi做内积得ki·(ηi,ηi) = 0 (向量两两正交,即对j ≠ i,有(ηj,ηi) = 0).又ηi ≠ 0...