Square root
From Simple English Wikipedia, the free encyclopedia
A square root of a number is the number that multiplied by itself gives the first number. For example, 2 is the square root of 4, because 
. Only numbers bigger than or equal to zero have real square roots, and a number bigger than zero has two square roots. One is positive (bigger than zero) and the other is negative (smaller than zero). There are two square roots because a negative number multiplied by a negative number is a positive number. Zero only has one square root: zero.
Square roots of negative numbers are not real numbers - they are imaginary. Every complex number except 0 has 2 square roots. For example: -1 has two square roots. We call them i and − i.
You write a square root by putting a bent line over a number, like this: 
. You say "the square root of 4" (or whatever number you are taking the square root of).
A whole number with a square root that is a whole number too 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...
