# Square Root of 391

In this article we're going to calculate the square root of 391 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 391 (both with and without a computer/calculator).

## Square Root of 391 Definition

In mathematical form we can show the square root of 391 using the radical sign, like this: √391. This is usually referred to as the square root of 391 in radical form.

So what is the square root? In this case, the square root of 391 is the quantity (which we will call q) that when multiplied by itself, will equal 391.

√391 = q × q = q2

## Is 391 a Perfect Square?

In math, we refer to 391 being a perfect square if the square root of 391 is a whole number.

In this case, as we will see in the calculations below, we can see that 391 is not 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 391 Rational or Irrational?

A common question is to ask whether the square root of 391 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 391 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 391 is a perfect square so we also can see that √391 is an irrational number.

## Can the Square Root of 391 Be Simplified?

391 can be simplified only if you can make 391 inside the radical symbol smaller. This is a process that is called simplifying the surd. In this example square root of 391 cannot be simplified.

## How to Calculate The Square Root of 391 with a Calculator

If you have a calculator then the simplest way to calculate the square root of 391 is to use that calculator. On most calculators you can do this by typing in 391 and then pressing the √x key. You should get the following result:

√391 ≈ 19.7737

## How to Calculate the Square Root of 391 with a Computer

On a computer you can also calculate the square root of 391 using Excel, Numbers, or Google Sheets and the SQRT function, like so:

SQRT(391) ≈ 19.773719933285

## What is the Square Root of 391 Rounded?

Sometimes you might need to round the square root of 391 down to a certain number of decimal places. Here are the solutions to that, if needed.

10th: √391 ≈ 19.8

100th: √391 ≈ 19.77

1000th: √391 ≈ 19.774

## What is the Square Root of 391 as a Fraction?

We covered earlier in this article that only a rational number can be written as a fraction, and irrational numbers cannot.

Like we said above, since the square root of 391 is an irrational number, we cannot make it into an exact fraction. However, we can make it into an approximate fraction using the square root of 391 rounded to the nearest hundredth.

√391

≈ 19.8/1

≈ 1977/100

≈ 19 77/100

## What is the Square Root of 391 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 391:

√b = b½

√391 = 391½

## How to Find the Square Root of 391 Using Long Division

Finally, we can use the long division method to calculate the square root of 391. 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 391 in pairs of two digits from right to left and attach one set of 00 because we want one decimal:

3
91
00

### Step 2

Starting with the first set: the largest perfect square less than or equal to 3 is 1, and the square root of 1 is 1 . Therefore, put 1 on top and 1 at the bottom like this:

 1 3 91 00 1

### Step 3

Calculate 3 minus 1 and put the difference below. Then move down the next set of numbers.

 1 3 91 00 1 2 91

### Step 4

Double the number in green on top: 1 × 2 = 2. Then, use 2 and the bottom number to make this problem:

2? × ? ≤ 291

The question marks are "blank" and the same "blank". With trial and error, we found the largest number "blank" can be is 9. Replace the question marks in the problem with 9 to get:

29 × 9 = 261

Now, enter 9 on top, and 261 at the bottom:

 1 9 3 91 00 1 2 91 2 61

### Step 5

Calculate 291 minus 261 and put the difference below. Then move down the next set of numbers.

 1 9 3 91 00 1 2 91 2 61 0 30 00

### Step 6

Double the number in green on top: 19 × 2 = 38. Then, use 38 and the bottom number to make this problem:

38? × ? ≤ 3000

The question marks are "blank" and the same "blank". With trial and error, we found the largest number "blank" can be is 7.

Now, enter 7 on top:

 1 9 7 3 91 00 1 2 91 2 61 0 30 00

That's it! The answer shown at the top in green. The square root of 391 with one digit decimal accuracy is 19.8. 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.