= ((x^2 + y^2)^2) \ ((x^2+y^2)-(x^2-y^2))((x^2+y^2)+(x^2-y^2)) = (x^2+y^2)^2 \ (x^2+y^2-x^2+y^2)(x^2+y^2+x^2-y^2)= (x^2+y^2)^2 \ 2y^2 *2x^2 = (x^2+y^2)^2 \ 4x^2* y^2 = x^4+2x^2y^2+y^4 \ 4x^2*y^2 = x^4\ 4x^2*y^2 + 2x^2*y^2 \ 4x^2* y^2 + y^4\ 4x^2* y^2= x^2\4y^2+1\2+y^2\4x^2