Guest: SIMPLIFY 9X+3Y
Hi Guest thank you for your contribution to this problem. I am sure that you were not the only one confused by my answer.
Hi guest, if you are asked to factorise 9X+3Y then the answer is indeed 3(3X-Y) So you can think of factorise as meaning 'put brackets in' if you like.
The factors are 3 and 3X-Y because when you multiply them together you get 9X+3Y
HOWEVER
The question says simplify. simplify means take away the brackets, not put them in!
Therefore 9X+3Y is already as SIMPLE as it can be.
+118654 
