Chapter 4 - Polynomials - 4.7 Polynomials in Several Variables - 4.7 Exercise Set - Page 284: 38

$2x^2-3xy+y^2$

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