# Help with Factorising Algebraic Expressions (1 Viewer)

#### HelloIAmGone

##### New Member
How do you factorise a2-b2-a+b?

The answers state (a-b)(a+b-1), and whilst trying to work out the question I got up to "(a+b)(a-b)-(a-b)" but have no idea on what to do next... complete mindblank rn x-x

#### InteGrand

##### Well-Known Member
How do you factorise a2-b2-a+b?

The answers state (a-b)(a+b-1), and whilst trying to work out the question I got up to "(a+b)(a-b)-(a-b)" but have no idea on what to do next... complete mindblank rn x-x
$\bg_white \noindent It's the same as how YX - X = X(Y-1) (where Y = a + b and X = a-b). In other words, factor out an (a-b) from each term in (a+b)(a-b) - (a-b).$

#### HeroWise

##### Active Member
$\bg_white (a+b)(a-b)-(a-b)=(a-b)(a+b-1)$

#### HelloIAmGone

##### New Member
Didn't think of that at all... thanks!