Answer
$-5x^3+8xy-9y^2$
Work Step by Step
Removing the grouping symbols and then combining like terms, the given expression, $
(x^3+7xy-5y^2)-(6x^3-xy+4y^2)
,$ simplifies to
\begin{array}{l}\require{cancel}
x^3+7xy-5y^2-6x^3+xy-4y^2
\\\\=
(x^3-6x^3)+(7xy+xy)+(-5y^2-4y^2)
\\\\=
-5x^3+8xy-9y^2
.\end{array}
