I have been stuck on factorizing this: \(\displaystyle a^2-2ab+a^2b-2b^2\).

I thought I could solve it by making \(\displaystyle (a+b)\) as one factor but it didn't work then I tried to add and deduct some terms which that didn't lead me to anything either.

I don't really know how what to next.

Any help would be greatly appreciated.