Question 374981


first remove the parentheses that are not needed from the expression. 
9x^2 - xy + y^2 - x^2 - 9xy + 3y^2

= 8x^2 - xy +y^2 - 9xy + 3y^2

Since -xy and -9xy are like terms, subtract 9xy from -xy to get -10xy. 

= 8x^2 - 10xy + y^2 + 3y^2


Since y^2 and 3y^2 are like terms, add 3y^2 to y^2 to get  4y^2

= answer: 8x^2 - 10xy + 4 y^2