In √a̅+̅b̅, the horizontal bar or vinculum is actually a parenthesis that groups a+b. Without it, √a+b might mean b+√a̅ or it might mean √a̅+̅b̅. Nevertheless, the square-root sign without the vinculum is often used .
Every complex number has two square roots; for example, the square roots of -4 are 2i and -2i.