Negative square root of 99

9.9498743710662 is the answer

The square root of a number A is another number B, such that B x B = A. B can be either positive or negative since - B x - B = A. The square root of 99 is re-written as 3 times the square root of 11 by factoring 99 as 9 x 11. The square root of 9 x 11 is the square root of 9 times the square root of 11. The square root of 9 is 3, and thus, the final answer is 3 times the square root of 11.