simplify: (4x^2 + 8xy + 2y^2) - (-9x^2 - 4xy - 7y^2)

first get ride of the second set of parenthesis by doing distributive property. 4x^2 + 8xy + 2y^2 + 9x^2 + 4xy + 7y^2 Then combine like terms.... 13x^2 + 8xy + 9y^2

4x^2+9x^2+2y^2+7y^2+8xy+4xy 12x^2 + 9y^2 + 11xy