计算分式x-y/x²+xy乘以x²y²-x的四次方/xy-x²
问题描述：
计算分式x-y/x²+xy乘以x²y²-x的四次方/xy-x²
答
原式=(x-y)/x(x+y)*[-x²(x²-y²)]/[-x(x-y)]
=(x-y)/x(x+y)*x²(x+y)(x-y)/x(x-y)
=(x-y)/x(x+y)*x(x+y)
=x-y