wa=aita.+ak, b=bi+bi+b, k ab=(ai+a,j+,k)( i +b,j+bk) ∵i⊥k,∵i·=j·k=k·i=0, LiEjEkE1, ∴i·i=j·j=k·k=1 b=++ b 数量积的坐标表达式a a i a j a k, x y z     = + + b bx i by j bzk     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