Answer
$3x^3+5x^2y-xy^2-8y^3$.
Work Step by Step
The given polynomials are
$-2x^3-x^2y+xy^2+7y^3$ and $x^3+4x^2y-y^3$.
$=x^3+4x^2y-y^3- (-2x^3-x^2y+xy^2+7y^3)$
Clear the parentheses.
$=x^3+4x^2y-y^3+2x^3+x^2y-xy^2-7y^3$
Add like terms.
$=3x^3+5x^2y-8y^3-xy^2$
Rearrange.
$=3x^3+5x^2y-xy^2-8y^3$.
