Answer:
9
Step-by-step explanation:
You want the square root of 81.
The square root (x) of a number (n) satisfies the relation ...
x² = n
Here, we want the value of x such that x² = 81.
We know from our memorization of multiplication tables that ...
9 × 9 = 9² = 81
That is, the square root of 81 is 9.
__
Additional comment
The square root symbol √ is used to signify the positive square root. We also know that (-9) × (-9) = 81, so another square root of 81 is -9.
Here the question asks for √81, the positive square root. When solving x²=81 by taking the square root of both sides of the equation, we must also consider that x may be negative:
x² = 81
x = ±√81 = ±9