(4) \( a^{2}-2 a+a b-2 b \)

Let's explore this expression! The expression \( a^{2}-2 a+a b-2 b \) can look a bit daunting at first. However, there's an opportunity to create some fun with factoring! You can rearrange and group the terms smartly: \( a^2 - 2a + ab - 2b \) can be factored as \( (a-2)(a+b) \) after careful manipulation. Now, think about the real-world implications! Anytime you're dealing with polynomials like this one, whether in physics for motion equations or in finance for modeling profits, understanding how to factor can simplify your calculations tremendously. The ability to manipulate these expressions helps decode complex problems and unveils the beauty of mathematics in everyday life!