What symbol is used to represent the square root of a negative number?

The symbol used to represent the square root of a negative number is 'i'. This symbol denotes the imaginary unit, which is defined as the square root of -1. In mathematics, when dealing with square roots of negative numbers, we use 'i' to express that the result is not a real number but an imaginary number. For example, the square root of -4 can be expressed as 2i, since √(-4) = 2√(-1) = 2i. This concept is fundamental in complex number theory, allowing representation and calculation involving imaginary and real parts. The other symbols mentioned do not convey this specific mathematical meaning, highlighting 'i' as the correct representation for the square root of negative numbers.