证明"→"S(x)=x TATAx-2baxtbb VS(x=2A Ax-2A b=0 "<"Vx=x"+6 4x-b2=|(x2+6)- =(4x*-b)+A8[(4x*-b)+A6 b+|4。+20A(Ax-b Ax-b+|4|2+26(4Ax-4b) Ax +|A6 可见,当δ=0时取到最小值" " S( x ) x A Ax b Ax b b T T T T 证明： = − 2 + S(x) = 2A Ax − 2A b = 0 T T ""  x = x * +δ 2 2 Ax b A( x ) b * − = +  − Ax b A A ( Ax b ) * T T * = − +  + 2 − 2 2 2 2 Ax b A * = − + 可见，当δ= 0时取到最小值. 2 ( ) 2 * 2 * Ax b A A Ax A b T T T = − +  +  − [(Ax * b) A ] [(Ax * b) A ] T = − + − +