Factor $9(a-1)^2 +3(a-1) - 2$ I got the equation $9(a-1)^2 +3(a-1) - 2$ on my homework sheet. I tried to factor it by making $(a-1)=a$ and then factoring as a messy trinomial. But even so, I couldn't  seem to get the correct answer; they all seemed incorrect. 
Any help would be greatly appreciated.
Thank you so much in advance! 

$\begin{align}{\bf Hint}\,\ {\rm  Let}\,\ x = 3(a\!-\!1).\ {\rm Then}\qquad &9(a\!-\!1)^2 +3(a\!-\!1)-2\\ =\ &x^2 + x - 2\\ =\ &(x+2)(x-1)\end{align}$
Remark $ $ Above is a special case of the AC-method, which gives a general way to change variables to transform polynomials to have leading coefficient $=1.\,$ This general method is well-worth learning since it often proves useful.
