Real number

A real number is a value that represents a quantity along a number line. Because they lie on a number line, their size can be compared. You can say one is greater or less than another, and do arithmetic with them in the usual way. All numbers you encounter in everyday life are real numbers*.

*Which numbers are not real?

• An imaginary number is a number whose square is negative. This can never happen with real numbers. See Imaginary numbers.
• Just as real numbers lie on a number line, complex numbers can be plotted on a 2-dimensional plane, and each need a pair of numbers to identify them - a real number and an imaginary number. See Complex numbers
• Numbers used as identifiers are not real numbers. Example: a driver's license number. These do not lie on the number line and it makes no sense to do arithmetic with them. Adding two license numbers is meaningless.

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