The root number 4 is equal to 2, and the square root of the root number 4 is also the square root of 2, which is √ 2; The arithmetic square root of radical number 4 is √2. The root sign is a mathematical symbol. The root sign is a symbol used to represent the root operation of a number or an algebra. If a? =b, then A is the n-th root of B or A is the 1/n power of B (n≠0).