d|-30·b+8|b|2=0 两式相减得46nb=23|b2 →ab=|b2 2 代入前式有|a|=b 故 i·b cos l‖!b a 2 元 (a, b)=arccos 237 | | 30 8 | | 0 2 2 a − a  b + b =     两式相减得 2 46a b 23 | b |     = 2 | | 2 1 a b b      = 代入前式有 | a | | b |   = 故 | || | cos( , ) a b a b a b        = 2 1 2 | | | | = = a b   2 3 1 ( , ) arccos  = =  a b  