求一个正交变换,把实二次型f（x1,x2,x3）=2X1x2+2X1x3-2X1X4-2X2X3+2X2X4+2X3X4化为标准型

A=0 1 1 -11 0 -1 11 -1 0 1-1 1 1 0|A-λE|=-λ 1 1 -11 -λ -1 11 -1 -λ 1-1 1 1 -λc1+c2+c3+c41-λ 1 1 -11-λ -λ -1 11-λ -1 -λ 11-λ 1 1 -λri-r1,i=2,3,41-λ 1 1 -10 -1-λ -2 20 -2 -λ-1 20 0 0 1-λ...