Square root facts for kids
In mathematics, a square root of a number x is another number that, when multiplied by itself (squared), becomes x. When it is nonnegative, it is represented by the symbol , and called the principal square root of x. 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.
An important number is the square root of 2, which is an irrational number. Its value is around 1.41421. It is also the length of a diagonal in the square whose side is 1.
Square roots of negative numbers are not real numbers – they are imaginary numbers. Imaginary numbers are basically numbers whose square is negative. Every complex number, except 0, has 2 square roots. For example, −1 has two square roots. We call them and . We also consider the number as the principal square root of −1, and called it the imaginary unit.
The sign for a square root is made by putting a bent line over a number, like this: . This is read as "the square root of 4" (or whatever number we are taking the square root of).
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.
Below is a table of square roots (rounded to 3 decimals places).
Number  Square root of number 

1  1.000 
2  1.414 
3  1.732 
4  2.000 
5  2.236 
6  2.449 
7  2.646 
8  2.828 
9  3.000 
10  3.162 
11  3.317 
12  3.464 
13  3.606 
14  3.742 
15  3.873 
16  4.000 
17  4.123 
18  4.243 
19  4.359 
20  4.472 
Origin of the symbol
It is not really known where the square root symbol comes from, but some people believe that it was from the letter r, which is the first letter of the Latin and German word radix. Radix means root or base. Thus, radix quadratum from Latin refer most likely to the base of a square. Since the sides of a square are all equal, the word radix may be interpreted as side of a square—without actually so.
Related pages
Images for kids

Constructing the length x=\sqrt{a}, given the a and the unit length
See also
In Spanish: Raíz cuadrada para niños
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