Ax=AX=(Ax)=(x)=入X 于是有 xAx=x(Ax)=x^x=入x'x xAx=(xA)x=(Ax)x=(入x)x=入xx 两式相减,得 (-)xx=0 但因x≠0,所以 x=∑xx=∑x1|≠0 故λ-x=0,即λ=,这就说明入为实数于是有 两式相减，得 但因x  0，所以 故 ，即 ，这就说明为实数。 Ax = Ax = (Ax) = (x) = x x x x x x x x x x x. x x x x x x x x,  =   =  =   =    =  =  =   A ( A ) (A ) ( ) A (A ) ( − )xx = 0 x x | x | 0, 2 n i 1 i n i 1  =  i i =   = = x x  −  = 0  = 