4/9x^2y^6-6xy^4+3/9x^2y^6=7/9x^2y^6-6xy^4
(-2/3xy^3)^2-3xy^4(2-1/9xy^2) =4/9x^2*y^6-6xy^4+1/3x^2y^6=7/9x^2*y^6-6xy^4