(x^2/y-3x-y^2/x)*(xy/x^2-y^2)=(x^2*xy)/(y*x^2)-(3x*xy)/x^2-(y^2*xy)/(x*x^2)-(x^2*y^2)/y+3xy^2+(y^2*y^2)/x=x^3y/x^2y-3x^2y/x^2-y^3x/x^3-x^2y+3xy^2+y^4/x=x-3y-y^3/x^2-x^2y+3xy^2+y^4/x
(x^2/y-3x-y^2/x)*(xy/x^2-y^2)=(x^2*xy)/(y*x^2)-(3x*xy)/x^2-(y^2*xy)/(x*x^2)-(x^2*y^2)/y+3xy^2+(y^2*y^2)/x=x^3y/x^2y-3x^2y/x^2-y^3x/x^3-x^2y+3xy^2+y^4/x=x-3y-y^3/x^2-x^2y+3xy^2+y^4/x