Question

已知（x+y）²=3,（x-y）²=,则[(xy+2)(xy-2)-2x²y²+

Answer 1

（x+y）²=3 (1)

（x-y）²=7,(2)

由(1)得x²+2xy+y²=3 (3)

由(2)得x²-2xy+y²=7 (4)

(3)-(4)得 4xy=-4

∴xy=-1

[(xy+2)(xy-2)-2x²y²+4]-1/2xy

=(-1+2)(-1-2)-2+4+1/2

=-3-2+4+1/2

=-1/2