Polynomials Question How Did They Get This Answer?

[Sarah P]

IN MathsQuest 3/4 the exercise is 1.2-Polynomials and the question is;

Fully factorise the following polynomials; 9x^2-xy-3x+y

in the answers they got (x-1)(3x-y), but how can that be??? Using grouping (as suggested by the book), i managed to get

=9x^2-3x-xy+y
=3x(3x-1)-y(x-1)

and thats as far as i can get! I checked my CAS and all that it gets is 9x^2-3x+y-xy

Is the answer in the book wrong or did i stuff up somewhere?!?! Any help would be greatly appreciated

[Peanut Butter]

I think that the textbook is wrong. If you expand their answer, you do not get the original expression.

Your answer is correct. It cannot be simplified further (hence why your calculator gave you the same answer)

[Sarah P]

I think that the textbook is wrong. If you expand their answer, you do not get the original expression.

Your answer is correct. It cannot be simplified further (hence why your calculator gave you the same answer)

Thanks for that  It's just a bit of a worrying sign for the textbook to have incorrect answers so early in the book!