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! 

$$9(a-1)^2 +3(a-1)-2=9(a^2-2a+1)+3a-3-2=$$
$$=9a^2-18a+9+3a-5=9a^2-15a+4=$$
$$(9a^2-1)-(15a-5)=(3a+1)(3a-1)-5(3a-1)=$$
$$(3a-1)(3a+1-5)=(3a-1)(3a-4)$$
