What Is the Square Root of 81?

The square root of 81 is 9. However, if a student needs to solve the equation  x2 = 81, then possible solutions can be either +9 or -9.


Because 81 is a perfect square, it is easy to find its square root. However, finding the square root of a number that is not a perfect square is more difficult. For example, the square root of 72 is 6 x √2. To find this answer, factor 72 into 2 x 36, all placed under the √ symbol, then factor out again as 2 x 6 x 6 (still under the √ symbol). As 36 is a perfect square, the 6s can be moved outside the √, resulting in the answer of 6√2.