You have the polynomial \(f(x,y)=-9xy^2 + 6x^2y - 5x^3\).
The additive inverse of a polynomial f(x,y) is a polynomial that makes zero when it added to polynomial f(x,y). So additive inverse of polynomial f(x,y) will be -f(x,y).
Thus, the additive inverse will be
\(-f(x,y)=9xy^2-6x^2y+5x^3\).
