Grouping factorisation This is the expression that I want to factorise ...
$4a^2 - b^2 + 4b - 4 $ 
I did my workings till - 
= $(2a+b)(2a-b) + 4(b-1) $ 
However I believe that this is not completely factorise .. Can I get a hint on where I started wrongly or how should I carry on from here ? Thanks ! 

You could do $4a^2-b^2+4b-4=4a^2-(b-2)^2=(2a-b+2)(2a+b-2)$  Whether this is more useful depends on your application.
