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Negative numbers are real numbers that are less than 0. Negative numbers are written with a minus sign "−" preceding the absolute value, e.g., −47. This can be thought of as a shorthand for 0 − 47.
Multiplying a negative number by −1 gives its absolute value, e.g., .
The square of a negative number is a positive number, and in fact ; but the square root of that negative number is a purely imaginary number of the form , where is the imaginary unit. For example, , but .