it a=ai +a,j+a, k, b=bi +b,j+b,k i·b (a i+a,j+a, k)bi+b,j+b, k) J a与⊥k,∴·j=jk=ki=0, liik=1 ∴i·i=j·j=k·k=1. d·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