it a=aita+ak, b=bi+bj+bk n·b元(a1+an+a2k)(b+b,j+b:k) 过k,∴·j=jk=k,i=0 iikE,,, j·j=k·k=1. a·b=abx+a,by+a2b 数量积的坐标表达式 上页a a i a j a k, x y z     = + + b b i b j b k x y z     设 = + + a  b =   (a i a j a k) x y z    + + (b i b j b k) x y z     + + i j k,     ⊥ ⊥ i  j = j  k = k i = 0,       | i |=| j |=| k |=1,     i i = j  j = k  k = 1.       x x y y z z a  b = a b + a b + a b   数量积的坐标表达式