The positive square root of 900 is 30. Similarly, the negative square root of 900 is -30. The positive square root, 30, is also known as the principal square root of 900.
The square root of 900 is any number, which when multiplied by itself, results in 900. Because 30*30 = 900 and (-30)*(-30) = 900, both 30 and -30 are considered square roots of 900.
Note that the square root of the product of two nonnegative numbers is equivalent to the product of the square roots of each number; in other words, sqrt(x*y) = sqrt(x)*sqrt(y) where x and y are greater than or equal to zero. This property allows one to more easily calculate the square root of 900 by hand, because 900 = 9*100. In this way, sqrt(900) = sqrt(9)*sqrt(100) = 3*10 = 30.