Chapter 4 - Polynomials - 4.7 Polynomials in Several Variables - 4.7 Exercise Set - Page 284: 41

$-2y^4x^3-2y^3x$

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