点积( dot product) a-b=a, +a2b2+a,b=2a, b,(34) aa=a2+a2a2=2a2+a|(35) 相互正交基矢( mutually orthogonal basis vectors) ji=八 0i≠ (36)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)