关于数量积的说明 (1)a·a=n 证∵6=0,∴·a=l‖ a cos 6=l (2)a·b=0÷→l⊥b 证(→):a·b=0,|a≠0,|b|≠0, c0s=0,=箕,∴a⊥b 2 (÷)alb,,8=;,:c0s6=0, n·b=l‖b|cos6=0. 上一页下一页现回关于数量积的说明： (2) a  b = 0    a b.   ⊥ () a  b = 0,    | a | 0,  | b | 0,  cos = 0, a b.    ⊥ (1) | | . 2 a a a     = () a b,    ⊥ cos = 0, a  b =| a || b | cos = 0.      = 0, | || | cos | | . 2 a a a a a      证   =  = 证  = , 2  , 2   =