7. \( 28 x^{3}-63 x b^{2} \)

Let's dive into some fun facts about this expression! Did you know that this polynomial can be factored? If we take out the common factor, which happens to be 7, we can rewrite this as \( 7(4x^{3} - 9xb^{2}) \). Factoring can help simplify problems in algebra and makes finding roots a piece of cake! Now, if you're ever faced with polynomial expressions like this, a common pitfall is forgetting to look for common factors initially. Always start by checking for shared coefficients and variables before attempting more complex factorizations. Trust me, it'll save you from unnecessary headaches later on!