[(x的平方+y的平方)-(x-y)的平方+2y(x-y)]÷4x
=(x²+y²-x²+2xy-y²+2xy-2y²)÷4x
=(4xy-2y²)÷4x
=2y(2x-y)÷4x
=-3y÷x
=-3(2x+6)÷x
=-6-18/x