取正交阵 52 15 √545 Q=(51,92,5) 153 0 A0=0AQ 10取正交阵 则 1 2 3 2 5 2 5 1 5 15 3 5 4 5 2 ( , , ) 5 15 3 5 2 0 3 3 Q        −     = =         −     1 1 1 10 Q AQ Q AQ −     = =       