The square root of 4 is +2 or -2. The square root of a number can be either positive or negative. This is because the square of +2 is 4 and the square of -2 is also 4.
Similarly, the square root of 9 is either +3 or -3, and the square root of 16 is either +4 or -4. The square root of any number is obtained from the square of a number. If a number is a perfect square, then it has a perfect square root. Numbers, such as 1, 4, 9 and 16 are all perfect squares, hence they have a perfect square root. Numbers such as 2, 3, 5, 6 and 7 are not perfect squares; therefore, their square roots are not whole numbers.