i a=a,+,+, k, b=bi+b,j+b,k b=(a i+a,j y +a2k)·(bi+b,j+b2k) jLk,∴i·j=j…k=k·i=0, i|j=k=1, i·i=jj=k·k=1 i·b=a.b.+a.b.+a.b x y J 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