= 1/(y+x)(y-x) + 1/(x+y)(x+y)
= 1/(y^2 - x^2) + 1/(x^2 + y^2)
= (x^2 + y^2 + y^2 - x^2) / (y^2 - x^2)(x^2 + y^2)
= 2y^2 / ((y-x)(y+x)(y+x)(y-x))
= 2y^2 / (y^2 - x^2)^2