令K = xA + (1-x)B = yC + (1-y)D (*) (x,y为实数)x(A-B) + B = y(C-D) + D (1)两边取共轭得x(*A-*B) + *B = y(*C-*D) + *D (2)联立(1) (2)解得x(A-B)(*A-*B) + B(*A-*B) = y(C-D)(*A-*B) + D(*A-*B)x(*A-*B)(A-B) +...