例2设x=(x1;…,xn),f(x)=x2x,求可,4 dxdx 解:f(x)=xx=∑x2, i=1 of=2x;,i=1,2,…,n df =2x dx =2(x1,x2y…,Xn), d!厂 =2x=2(x1,x2,…,xn) d →2. ( , , ) , ( ) , , . 1 T T n T df df x x x f x x x dx dx 例 设 求 = = 2 1 : ( ) , n T i i f x x x x = 解 = =  2 , 1,2, , . i i f x i n x  = =  1 2 1 2 2 2( , , , ) , 2 2( , , , ). T n T T n df x x x x dx df x x x x dx = = = =