√ Mathematically called "root sign", which means to find the arithmetic square root of a number. (that is, the square is equal to the positive number of this number). Negative numbers have no arithmetic square root. The arithmetic square root of the real number a is written as, where a≥0 is defined as ≥0.

For example, because, so. In particular, it is stipulated that the arithmetic square root of 0 is 0.

Although negative numbers have no arithmetic square root, they have square roots in the range of complex numbers (note! The arithmetic square root is different from the square root. For example, the arithmetic square root of 25 is only 5, but there are two square roots, that is, 5), here is the "imaginary unit". After introducing imaginary number, the square root of any negative number can be expressed by a quadratic root with I, for example.