Answer
$-5x^3+8xy-9y^2$
Work Step by Step
Consider the given polynomial
$(x^3+7xy-5y^2)-(6x^3-xy+4y^2)$
Need to drop the parentheses and will have to change the sign of each term of the second polynomial because of the presence of the negative outside.
Thus,
$(x^3+7xy-5y^2)-(6x^3-xy+4y^2)=x^3+7xy-5y^2-6x^3+xy-4y^2$
or, $=x^3-6x^3+7xy-xy-5y^2-4y^2$
or, $=-5x^3+8xy-9y^2$
