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VCE Stuff => VCE Mathematics => VCE Mathematics/Science/Technology => VCE Subjects + Help => VCE Mathematical Methods CAS => Topic started by: Sarah P on January 18, 2016, 04:48:07 pm

Title: Polynomials Question How Did They Get This Answer?
Post by: Sarah P on January 18, 2016, 04:48:07 pm

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

Title: Re: Polynomials Question How Did They Get This Answer?
Post by: Peanut Butter on January 18, 2016, 04:57:01 pm

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) :)

Title: Re: Polynomials Question How Did They Get This Answer?
Post by: Sarah P on January 18, 2016, 05:18:20 pm

Quote from: Peanut Butter on January 18, 2016, 04:57:01 pm

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