线段的长度 P(X1,x2) (X,X)=X12+X2+….+x2≥0 若爷ⅹ=(x1X2),则 OP|=√x2+ 若爷X=(X1,X2,X3),则 OP=√x2+x2+x3 O线段的长度 2 2 1 2 | | [ , ] OP x x x x = + = x1 x2 P(x1, x2) O 若令 x = (x1, x2)T，则 (x, x) = x12 + x22 + … + xn2 ≥ 0 x1 x2 x3 P O 2 2 2 1 2 3 | | [ , ] OP x x x x x = + + = 若令 x = (x1, x2, x3)T，则