# Square Root of 81

In this article we're going to calculate the square root of 81 and explore what the square root is and answer some of the common questions you might. We'll also look at the different methods for calculating the square root of 81 (both with and without a computer/calculator).

## Square Root of 81 Definition

In mathematical form we can show the square root of 81 using the radical sign, like this: √81. This is usually referred to as the square root of 81 in radical form.

Want to quickly learn or refresh memory on how to calculate square root play this quick and informative video now!

So what is the square root? In this case, the square root of 81 is the quantity (which we will call q) that when multiplied by itself, will equal 81.

√81 = q × q = q2

## Is 81 a Perfect Square?

In math, we refer to 81 being a perfect square if the square root of 81 is a whole number.

In this case, as we will see in the calculations below, we can see that 81 is a perfect square.

To find out more about perfect squares, you can read about them and look at a list of 1000 of them in our What is a Perfect Square? article.

## Is The Square Root of 81 Rational or Irrational?

A common question is to ask whether the square root of 81 is rational or irrational. Rational numbers can be written as a fraction and irrational numbers cannot.

A quick way to check this is to see if 81 is a perfect square. If it is, then it is a rational number. If it's not a perfect square then it's an irrational number.

We already know if 81 is a perfect square so we also can see that √81 is a rational number.

## Can the Square Root of 81 Be Simplified?

Since 81 is a perfect square it can be simplified because the result will always be equal to a whole number. Let's simplify the square root of 81:

√81 = 9.

## How to Calculate The Square Root of 81 with a Calculator

If you have a calculator then the simplest way to calculate the square root of 81 is to use that calculator. On most calculators you can do this by typing in 81 and then pressing the √x key. You should get the following result:

√81 = 9

## How to Calculate the Square Root of 81 with a Computer

On a computer you can also calculate the square root of 81 using Excel, Numbers, or Google Sheets and the SQRT function, like so:

SQRT(81) = 9

## What is the Square Root of 81 Written with an Exponent?

All square root calculations can be converted to a number (called the base) with a fractional exponent. Let's see how to do that with the square root of 81:

√b = b½

√81 = 81½

## How to Find the Square Root of 81 Using Long Division

Finally, we can use the long division method to calculate the square root of 81. This is very useful for long division test problems and was how mathematicians would calculate the square root of a number before calculators and computers were invented.

### Step 1

Set up 81 in pairs of two digits from right to left and attach one set of 00 because we want one decimal:

81

### Step 2

Starting with the first set: the largest perfect square less than or equal to 81 is 81, and the square root of 81 is 9 . Therefore, put 9 on top and 81 at the bottom like this:

 9 81 81

That's it! The answer shown at the top in green. The square root of 81 with one digit decimal accuracy is 9. Notice that the last two steps actually repeat the previous two. To add decimal places to your answe you can simply add more sets of 00 and repeat the last two steps.