21 记P=(PP2PP PAP= 2100 A(P,P,P,P)=(P,B,B,B)0210 0020 有AR=2R,A=2 0002 4P2=B1+2P2, 也即(A-2)=0, AB=B2+2P3, (A-2DB=1, 解(A-21)X=0, (A-2)3=P8 . 2 2 2 1 2 1 1             = − P AP ( ). 记 P = P1 P2 P3 P4 . 0 0 0 2 0 0 2 0 0 2 1 0 2 1 0 0 ( , , , ) ( , , , ) 1 2 3 4 1 2 3 4             A P P P P = P P P P 2 , 2 , 2 , 2 . 3 2 3 2 1 2 1 1 4 4 AP P P AP P P AP P AP P = + = + 有 = = 解(A−2I)X = 0, ( 2 ) , ( 2 ) , ( 2 ) 0, 3 2 2 1 1 A I P P A I P P A I P − = − = 也即 − =