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= 21

The square root of a number is that number which, when multiplied by itself will equal the original number.

√441= 21A square root of a number is another number that, when it is multiplied by itself (squared), gives the first number again. For example, 2 is the square root of 4, because 2×2=4. Only numbers bigger than or equal to zero have real square roots. The only square root of zero is zero.

Square roots of negative numbers are not real numbers – they are imaginary numbers. Imaginary numbers are basically numbers that cannot be square rooted and get a real result. Every complex number except 0 has 2 square roots. For example: −1 has two square roots. We call it i and -i.

A whole number with a square root that is also a whole number is called a perfect square. The first few perfect squares are: 0, 1, 4, 9, 16, 25, 36, 49, 64, 81, 100, 121, 144, 169, 196, 225, 256, 289, 324, 361, 400, 441, 484, 529, 576, 625, 676, 729, 784, 841, 900, 961, 1024, 1089, 1156, 1225 etc.