How to factorise this expression $ x^2-y^2-x+y$ This part can be factorised as  $x^2-y^2=(x+y)(x-y)$, How would the rest of the expression be factorised ?
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You can observe that $-x+y = -(x-y)$. So both $x^2-y^2$ and $-x+y$ have $x-y$ as a factor. You can use these info to get below factorization
$$
x^2 + y^2 - x +y = (x+y)(x-y)-(x-y) = (x+y-1)(x-y)
$$
