x+y=-2,xy=1；求代数式x⁴+y⁴-2x²y²的值.x⁴+y⁴-2x²y²=(x²-y²)²=[(x+y)(x-y)]²=4(x-y)²=4(x²-2xy+y²)=4[(x+y)²-4xy)]=4(4-4)=0...