How do you get the answer to the square root of 21?

Answer 1

In the olden days (1970's), we had charts to look up square roots that weren't perfect squares. ...or we memorized the ones that came up a lot like square root of 2 and 3.

Now (2012) you can just use a calculator: type in 21, then press the square root button which looks like a check mark with a horizontal line coming out from the top of the check mark. Sometimes it has an x under the horizontal line.

The answer will be in the calculator display.

OR...

If you know the perfect squares you can do a rudimentary calculation. 21 is between 16 and 25, so the answer will be between 4 and 5. Then you can do check and guess to get closer: 4.5 squared = 20.25, and 4.6 squared = 21.16, so the answer will be slightly more than 4.5. Now try 4.58 squared, which is 20.9764 & 4.59 squared is over 21, so the answer is between 4.58 & 4.59.

...and so on.