When you multiply a real or complex number by itself, you are actually squaring that number. Mathematicians express the square of a number using the superscript 2, or, for example, 2². The square of a real number is always positive, whether the number is 2² (= 4) or -2² (= 4; a negative times a negative equals a positive real number).

A square root is a number that when multiplied by itself equals a specific product. For example, if t² = s, then , in which t is the square root and s is a positive number. For example, the two square roots of are 4 and -4, as 4² = 16 and -4² = 16.