Question 478946
you can only add "like" nomials, like, xy^2 + xy^2     or  a^2 + a^2    

not   ab^2 + ab^3     or  xy + ab^2      

soooo...

(5x^2-xy+y^2) + (-x^2-9xy+8y^2)    for the answer, i will put them in decending order

9y^2+4x^2-10xy