√-1 is defined as i), for the vast majority of problems and discussions in school-level math, we stick to real numbers. So, if x is any real number, then √x is only defined if x ≥ 0. If x < 0, then √x is invalid for real numbers.Now, this rule gets a little more interesting, and sometimes trickier, when we're dealing with nested radical expressions. These are those intimidating-looking scenarios where you have a square root inside another square root, perhaps even several layers deep! The key here is to work your way from the inside out. You have to ensure that every single radicand (the number or expression inside the square root symbol) is non-negative at each step of the simplification or evaluation process. If at any point, working from the innermost root, you encounter a negative number trying to sneak under a square root, then the entire expression becomes invalid within the real number system.It's like peeling an onion, guys. You start with the very core. If that core piece is rotten (negative), then the whole onion (the entire expression) is no good. You can't just ignore it and move to the next layer. You must evaluate the innermost expression first. Is √ (5 - √30) valid? First, you check √30. That's fine. Then you check 5 - √30. If 5 - √30 turns out to be negative, then √ (5 - √30) is invalid. Conversely, if 5 - √30 is positive or zero, then the outer square root can be taken, and the expression makes sense. This methodical approach is your best friend when deciphering complex radical puzzles. Always take a deep breath, break it down, and check each layer against our golden rule. This systematic check not only helps you identify invalid expressions but also strengthens your overall analytical skills. Remember, precision and attention to detail are your greatest assets when dealing with these mathematical structures, preventing common errors and ensuring the integrity of your calculations.