设二次型f的矩阵A=【2 0 -1,0 1 0,-1 0 1】则f(x1,x2,x3)等于?

问题描述:

设二次型f的矩阵A=【2 0 -1,0 1 0,-1 0 1】则f(x1,x2,x3)等于?

2(x1)^2-2(x1*x3)+(x2)^2+(x3)^2