AA^-1=I-aa^T+(1/x)aa^T-(1/x)a(a^Ta)a^T=I-aa^T+(1/x)aa^T-(1/x)a(2x^2)a^T=I
(-1+1/x-2x)=0;2x^2+x-1=0,x1=-1,x2=1/2,由已知x