点积(dot product) a-b=ab+aba +ab;=abr (3.4) aa=a+a+a=∑aa (3.5) 相互正交基矢(mutually orthogonal basis vectors)) 说-4-a=6小 (3.6) 点积(dot product) i i a b = a b + a b + a b = ai b → → 1 1 2 2 3 3 2 2 2 3 2 2 2 | | 1  → → →  = + + = = i a a a a a ai a (3.4) (3.5) 相互正交基矢(mutually orthogonal basis vectors)        =  = = = → → if i j if i j e e i j i j j i 0 1   (3.6)