>>40
(略解)
A = (a b)
  (c d)
A-E ≠ O,
|A-E| = (a-1)(d-1) - bc = |A| - (a+d) +1 = 0,
とするとき、不動点は
 ( x ) = ( b ), (1-d)
 ( y )  (1-a), ( c )