Question 166364
{{{(9x^4 + 3xy - y^3) - (x^4 + 7xy + 3y^3)=9x^4 + 3xy - y^3 - x^4 - 7xy - 3y^3=(9x^4- x^4) + (3xy- 7xy)+(-3y^3- y^3)=8x^4-4xy-4y^3}}}