原式=(x+y)/(x+y)(x-y)-(2x-y)/(4x²-4xy+y²)
=1/(x-y)-(2x-y)/(2x-y)²
=1/(x-y)-1/(2x-y)
=(2x-y-x+y)/(x-y)(2x-y)
=x/(2x²-3xy+y²)