已知x+y=6,xy=-2,求（x的4次方-y的4次方）除以x²+y²/xy除以（6x-6y)的值

题目

已知x+y=6,xy=-2,求（x的4次方-y的4次方）除以x²+y²/xy除以（6x-6y)的值

答案

原式=(x²+y²)(x²-y²)*xy/(x²+y²)÷(6x-6y)
=xy(x+y)(x-y)÷6(x-y)
=xy(x+y)/6
=-2×6/6
=-2