There are a couple of different algorithms. The simplest one (the one that is used for computers), you take a guess:
1. Given: N (75 in this case)
2. Guess: 8.5 (because 8*8 is 64 and 9*9 is 81)
3. Divide 75 by 8.5 = 8.8235
4. Average the guess with the dividend in #3 (8.5 + 8.8235) / 2 = 8.66176
5. Use the value obtained in #4 as the new divisor (the new guess) in item #3. (75 / 8.66176 = 8.65874).
repeat until the averaged value is the same as the guess within the desired accuracy.
The second algorithm seems more complicated -- but I learned it in junior high school. I started to describe it and realized that I'd need a lot more space and time to describe it in a manner that would be understood. I then googled this link.
http://www.homeschoolmath.net/teachi...-algorithm.php
If you really want to know this algorithm, look at this link.
Here's another example.
http://www.homeschoolmath.net/teachi...hm-example.php