回顾:线段的长度k,x=x2+x2+…+x20 192 若令x=(x1,x2)T,则 OP=√x2+x 若令x=(x1 1,x2,x3) 则 2 OP=x+场+回顾：线段的长度 2 2 1 2 | | [ , ] OP x x x x = + = x1 x2 x1 x2 x3 P(x1 , x2 ) O P O 若令 x = (x1 , x2 ) T，则 222 1 2 3 | | [ , ] OP x x x x x = + + = 若令 x = (x1 , x2 , x3 ) T，则 [x, x] = x1 2 + x2 2 + … + xn 2 ≥ 0